# Convertitive

> Free instant converters for length, weight, temperature, currency, color, code, BMI, and more — 745 tools across 24 categories. No signup, no clutter.

All calculations run client-side in the browser. No accounts, no API keys, no data leaves the user's device. Unit factors are exact per NIST SP 811 and the 1959 international yard and pound agreement; currency rates come from the European Central Bank via Frankfurter (refreshed hourly).

## Most popular tools
- [Length: cm → inches](https://convertitive.com/length/cm-to-inches/)
- [Weight: kg → lb](https://convertitive.com/weight/kg-to-lb/)
- [Temperature: celsius → fahrenheit](https://convertitive.com/temperature/celsius-to-fahrenheit/)
- [Length: m → feet](https://convertitive.com/length/m-to-feet/)
- [Length: miles → km](https://convertitive.com/length/miles-to-km/)
- [Volume: liters → us-gallons](https://convertitive.com/volume/liters-to-us-gallons/)
- [Speed: kmh → mph](https://convertitive.com/speed/kmh-to-mph/)
- [Pressure: bar → psi](https://convertitive.com/pressure/bar-to-psi/)
- [Energy: kcalories → kjoules](https://convertitive.com/energy/kcalories-to-kjoules/)
- [Power: kilowatts → hp-mechanical](https://convertitive.com/power/kilowatts-to-hp-mechanical/)

## Unit conversion
- [Length](https://convertitive.com/length/) — mm, cm, m, km, in, ft, yd, mi, nmi, ly, pc, Å
- [Weight](https://convertitive.com/weight/) — g, kg, t, oz, lb, st
- [Temperature](https://convertitive.com/temperature/) — °C, °F, K
- [Volume](https://convertitive.com/volume/) — mL, L, gal, gal (UK), fl oz, cup, pt, tbsp, tsp
- [Speed](https://convertitive.com/speed/) — m/s, km/h, mph, kn
- [Time](https://convertitive.com/time/) — s, min, h, d, wk, yr
- [Pressure](https://convertitive.com/pressure/) — Pa, kPa, MPa, bar, atm, psi, mmHg, Torr, mbar
- [Energy](https://convertitive.com/energy/) — J, kJ, cal, kcal, Wh, kWh, BTU, eV
- [Power](https://convertitive.com/power/) — W, kW, MW, hp, PS, BTU/h
- [Data size](https://convertitive.com/data/) — bit, B, kB, MB, GB, TB, KiB, MiB, GiB, TiB
- [Torque](https://convertitive.com/torque/) — N·m, kN·m, lb-ft, lb-in, kgf·m, dyn·cm

## Currency
- [All 50 live currency pairs](https://convertitive.com/currency/) — ECB mid-market rates, refreshed hourly
- [USD to EUR](https://convertitive.com/currency/usd-to-eur/)
- [GBP to USD](https://convertitive.com/currency/gbp-to-usd/)
- [USD to TRY](https://convertitive.com/currency/usd-to-try/)
- [EUR to GBP](https://convertitive.com/currency/eur-to-gbp/)

## Color
- [All color converters](https://convertitive.com/color/) — HEX ↔ RGB ↔ HSL ↔ HSV with live swatch preview
- [HEX to RGB](https://convertitive.com/color/hex-to-rgb/)
- [RGB to HEX](https://convertitive.com/color/rgb-to-hex/)
- [HSL to HEX](https://convertitive.com/color/hsl-to-hex/)

## Number bases
- [All base converters](https://convertitive.com/number/) — binary, octal, decimal, hexadecimal (arbitrary precision via BigInt)
- [Roman numeral converter](https://convertitive.com/number/roman/) — 1 to 3,999,999

## Code & developer tools
- [Code tools index](https://convertitive.com/code/)
- [Base64 encode / decode](https://convertitive.com/code/base64/) — supports standard + base64url
- [URL encode / decode](https://convertitive.com/code/url-encode/) — RFC 3986
- [JSON ↔ YAML](https://convertitive.com/code/json-yaml/)
- [Case converter](https://convertitive.com/code/case/) — camel / snake / kebab / Pascal / etc.
- [JWT decoder](https://convertitive.com/code/jwt-decoder/)
- [UUID generator](https://convertitive.com/code/uuid/) — v4 and v7
- [Hash generator](https://convertitive.com/code/hash/) — SHA-1, SHA-256, SHA-384, SHA-512
- [Lorem ipsum generator](https://convertitive.com/code/lorem-ipsum/)
- [Word + character counter](https://convertitive.com/code/word-counter/)
- [Password generator](https://convertitive.com/code/password-generator/) — crypto-strong, live entropy meter
- [Cron expression generator & parser](https://convertitive.com/code/cron-expression/) — plain-English description, next 5 runs, 11 presets
- [Unix timestamp converter](https://convertitive.com/code/timestamp-converter/) — s / ms / μs / ns, auto-detect, batched paste, ISO 8601 + RFC 3339

## Image format
- [Image converters](https://convertitive.com/image/) — PNG ↔ JPG ↔ WebP, browser-only
- [Image to Base64](https://convertitive.com/image/base64/) — drag and drop, no upload

## Health
- [Health tools](https://convertitive.com/health/)
- [BMI calculator](https://convertitive.com/health/bmi/) — metric / imperial, WHO categories
- [BMR & TDEE](https://convertitive.com/health/bmr/) — Mifflin-St Jeor, 5 activity levels
- [Body fat percentage](https://convertitive.com/health/body-fat/) — US Navy tape method
- [Pregnancy due date](https://convertitive.com/health/due-date/) — Naegele's rule, weeks + trimester
- [Macro calculator](https://convertitive.com/health/macro-calculator/) — daily kcal + protein/carbs/fat, Mifflin-St Jeor + 4 macro presets
- [Calories burned](https://convertitive.com/health/calories-burned/) — Compendium MET tables, 22 activities × 3 intensity levels

## Date & time
- [Date / time calculators](https://convertitive.com/datetime/)
- [Age calculator](https://convertitive.com/datetime/age-calculator/) — years, months, days from DOB
- [Date difference](https://convertitive.com/datetime/date-difference/) — days / weeks / months between two dates
- [Working days counter](https://convertitive.com/datetime/working-days/) — Mon-Fri between two dates
- [Time zone converter](https://convertitive.com/datetime/timezone/) — 28 zones with DST handled automatically
- [Days until any date](https://convertitive.com/datetime/days-until/) — live countdown to Christmas, New Year, any named event, or any ISO date

## Math
- [Math calculators](https://convertitive.com/math/)
- [Percentage calculator](https://convertitive.com/math/percentage/) — % of, is what %, and signed change
- [Area calculator](https://convertitive.com/math/area/) — 8 shapes incl. Heron's-formula triangles

## Finance
- [Finance calculators](https://convertitive.com/finance/)
- [Mortgage calculator](https://convertitive.com/finance/mortgage/) — monthly payment + total interest
- [Compound interest](https://convertitive.com/finance/compound-interest/) — with periodic contributions
- [Tip calculator](https://convertitive.com/finance/tip/) — bill split + optional sales tax
- [Sales tax](https://convertitive.com/finance/sales-tax/) — add tax + reverse pre-tax
- [Discount calculator](https://convertitive.com/finance/discount/) — single or multiplicative-stacked
- [Auto loan calculator](https://convertitive.com/finance/auto-loan/) — payment + interest + amortization with sales tax + trade-in
- [Loan payoff calculator](https://convertitive.com/finance/loan-payoff/) — months to payoff + interest saved with extra payments

## Crypto
- [Crypto unit converters](https://convertitive.com/crypto/)
- [Wei / Gwei / ETH](https://convertitive.com/crypto/wei-gwei-eth/) — exact BigInt math, no precision loss

## Sizes
- [Size converters](https://convertitive.com/sizes/)
- [Shoe size](https://convertitive.com/sizes/shoe/) — US/UK/EU/JP, men/women/kids
- [Bra size](https://convertitive.com/sizes/bra/) — modern band-rounding method, US/UK/EU
- [Ring size](https://convertitive.com/sizes/ring/) — US/UK/EU/JP from diameter or circumference

## Design
- [Design tools](https://convertitive.com/design/)
- [Aspect ratio](https://convertitive.com/design/aspect-ratio/) — reduce + scale + live preview
- [DPI / PPI](https://convertitive.com/design/dpi/) — pixel + physical size with device presets

## Cooking
- [Cup ↔ grams](https://convertitive.com/cooking/) — per-ingredient density for 36 ingredients
- [Oven temperature](https://convertitive.com/cooking/oven-temperature/) — °C / °F / UK Gas Mark

## AI tools
- [AI token counter & API cost](https://convertitive.com/ai/token-counter/) — GPT, Claude, Gemini, Llama pricing
- [LLM cost calculator](https://convertitive.com/ai/llm-cost-calculator/) — 15 models, per-call + monthly projection, workload presets, comparison table
- [Context window visualizer](https://convertitive.com/ai/context-window-visualizer/) — 16 models, paste-and-see fill bars, GPT-4o (128K) to Gemini 1.5 Pro (2M)

## Auto
- [Fuel economy](https://convertitive.com/fuel-economy/) — MPG ↔ L/100km ↔ km/L, inverse-aware

## Editorial guides
- [/guides/15-year-vs-30-year-mortgage/](https://convertitive.com/guides/15-year-vs-30-year-mortgage/) — Side-by-side amortization math comparing total interest and payment shock for both terms.
- [/guides/how-to-read-a-mortgage-amortization-schedule/](https://convertitive.com/guides/how-to-read-a-mortgage-amortization-schedule/) — Line-by-line walkthrough of an amortization table: principal, interest, and remaining balance.
- [/guides/how-much-house-can-i-afford/](https://convertitive.com/guides/how-much-house-can-i-afford/) — Front-end and back-end DTI ratios with worked numbers from real US lender thresholds.
- [/guides/mortgage-refinance-break-even/](https://convertitive.com/guides/mortgage-refinance-break-even/) — Break-even months formula weighing closing costs against monthly savings after refinance.
- [/guides/compound-interest-explained/](https://convertitive.com/guides/compound-interest-explained/) — Annual vs continuous compounding derived from first principles with contribution examples.
- [/guides/how-to-calculate-tdee-correctly/](https://convertitive.com/guides/how-to-calculate-tdee-correctly/) — Mifflin-St Jeor BMR plus activity multipliers, with common pitfalls in self-reporting.
- [/guides/bmi-vs-body-fat-percentage/](https://convertitive.com/guides/bmi-vs-body-fat-percentage/) — Why BMI misclassifies muscular and elderly bodies, and which method fits which goal.
- [/guides/is-bmi-accurate/](https://convertitive.com/guides/is-bmi-accurate/) — Population-level vs individual accuracy of BMI and where the 25/30 cutoffs came from.
- [/guides/how-pregnancy-due-dates-are-calculated/](https://convertitive.com/guides/how-pregnancy-due-dates-are-calculated/) — Naegele's rule, LMP vs ultrasound dating, and why the 280-day estimate has wide variance.
- [/guides/how-to-measure-your-bra-size/](https://convertitive.com/guides/how-to-measure-your-bra-size/) — Modern band-rounding method with tape placement and common sister-size adjustments.
- [/guides/meat-temperature-safety/](https://convertitive.com/guides/meat-temperature-safety/) — USDA internal cooking temperatures for poultry, beef, pork, and fish with carryover heat.
- [/guides/converting-cups-to-grams-baking/](https://convertitive.com/guides/converting-cups-to-grams-baking/) — Why volume measures fail for flour and how density tables fix recipe reproducibility.
- [/guides/converting-historical-recipes/](https://convertitive.com/guides/converting-historical-recipes/) — Translating old units (gill, peck, dram, slow oven) into modern grams and °C.
- [/guides/recipe-scaling-beyond-2x/](https://convertitive.com/guides/recipe-scaling-beyond-2x/) — Non-linear scaling rules for pans, leavening, salt, and bake time beyond a simple doubling.
- [/guides/gas-mark-conversion-table/](https://convertitive.com/guides/gas-mark-conversion-table/) — UK Gas Mark to °C/°F with the original 1933 Regulo correspondence.
- [/guides/how-tipping-works-around-the-world/](https://convertitive.com/guides/how-tipping-works-around-the-world/) — Country-by-country tipping norms for restaurants, taxis, and hotels with rate ranges.
- [/guides/tip-in-cashless-restaurants/](https://convertitive.com/guides/tip-in-cashless-restaurants/) — How tip prompts on POS screens distort tipping behavior and what to do at 0%.
- [/guides/vat-vs-sales-tax/](https://convertitive.com/guides/vat-vs-sales-tax/) — Tax-inclusive EU VAT vs tax-exclusive US sales tax with reverse-calculation examples.
- [/guides/what-percent-discount-is-actually-good/](https://convertitive.com/guides/what-percent-discount-is-actually-good/) — Anchor pricing, stacked discounts, and the multiplicative math behind '50% off plus 20%'.
- [/guides/historical-currency-conversion/](https://convertitive.com/guides/historical-currency-conversion/) — ECB reference rate sources, weekend gaps, and how to reproduce a past-date conversion.
- [/guides/what-5-years-of-ecb-rates-show/](https://convertitive.com/guides/what-5-years-of-ecb-rates-show/) — EUR/USD volatility trends 2020-2025 and what they imply for cross-border pricing.
- [/guides/salary-by-city/](https://convertitive.com/guides/salary-by-city/) — Cost-of-living adjustments via PPP for comparing offers across US and EU metros.
- [/guides/how-cryptocurrency-mining-actually-works/](https://convertitive.com/guides/how-cryptocurrency-mining-actually-works/) — Proof-of-work hashing, block rewards, and why ETH moved to proof-of-stake.
- [/guides/wei-gwei-eth-explained/](https://convertitive.com/guides/wei-gwei-eth-explained/) — The three Ethereum denominations and when BigInt math is mandatory for gas estimates.
- [/guides/how-gpt-tokenization-actually-works/](https://convertitive.com/guides/how-gpt-tokenization-actually-works/) — BPE merges, special tokens, and why 'strawberry' costs more tokens than 'cat'.
- [/guides/how-token-pricing-works-for-llm-apis/](https://convertitive.com/guides/how-token-pricing-works-for-llm-apis/) — Input vs output token billing across OpenAI, Anthropic, Google with cost-per-1k tables.
- [/guides/how-to-pick-a-strong-password/](https://convertitive.com/guides/how-to-pick-a-strong-password/) — Entropy bits, dictionary attacks, and why length beats character-class requirements.
- [/guides/css-color-formats-hex-vs-hsl/](https://convertitive.com/guides/css-color-formats-hex-vs-hsl/) — When to reach for hex, rgb(), hsl(), or oklch() in a modern stylesheet.
- [/guides/color-contrast-for-accessibility/](https://convertitive.com/guides/color-contrast-for-accessibility/) — WCAG 2.1 AA/AAA ratios with relative luminance formula and pass/fail examples.
- [/guides/png-vs-jpg-vs-webp/](https://convertitive.com/guides/png-vs-jpg-vs-webp/) — Lossless vs lossy compression and which format wins for screenshots, photos, and UI.
- [/guides/how-to-resize-images-without-quality-loss/](https://convertitive.com/guides/how-to-resize-images-without-quality-loss/) — Bicubic vs Lanczos resampling and the upper limit beyond which any resize degrades.
- [/guides/aspect-ratios-for-video/](https://convertitive.com/guides/aspect-ratios-for-video/) — 16:9, 9:16, 4:5, 1:1 across YouTube, Reels, TikTok, and stories with safe-area notes.
- [/guides/dpi-vs-ppi-vs-density/](https://convertitive.com/guides/dpi-vs-ppi-vs-density/) — Print DPI vs screen PPI vs CSS px density-independence with device-pixel-ratio examples.
- [/guides/shoe-size-by-manufacturer/](https://convertitive.com/guides/shoe-size-by-manufacturer/) — Why Nike US 10 ≠ Adidas US 10 and how Brannock + Mondopoint solve the chaos.
- [/guides/ring-size-by-mail-without-a-ring/](https://convertitive.com/guides/ring-size-by-mail-without-a-ring/) — Paper-strip and printable circle methods with the +/- 0.4 mm tolerance to expect.
- [/guides/area-of-irregular-shape/](https://convertitive.com/guides/area-of-irregular-shape/) — Decomposition, Heron's formula, and the surveyor's shoelace formula for polygons.
- [/guides/percentage-vs-percentage-point-difference/](https://convertitive.com/guides/percentage-vs-percentage-point-difference/) — Why a rate going from 5% to 6% is 'one point' but 20% relative — a common reporter error.
- [/guides/why-percentage-change-isnt-percentage-difference/](https://convertitive.com/guides/why-percentage-change-isnt-percentage-difference/) — Asymmetric vs symmetric formulas and when each is the correct denominator.
- [/guides/mean-median-mode-when-to-use-each/](https://convertitive.com/guides/mean-median-mode-when-to-use-each/) — Skewed distributions, outliers, and why median beats mean for income and home prices.
- [/guides/standard-deviation-explained/](https://convertitive.com/guides/standard-deviation-explained/) — Population vs sample formulas, Bessel's correction, and the 68-95-99.7 empirical rule.
- [/guides/roman-numeral-conventions/](https://convertitive.com/guides/roman-numeral-conventions/) — Subtractive notation, the vinculum for thousands, and why MMMM is rarely used.
- [/guides/why-metric-units-won-everywhere-except-the-us/](https://convertitive.com/guides/why-metric-units-won-everywhere-except-the-us/) — Historical and political reasons SI is universal and US customary persists.
- [/guides/date-difference-for-visa-applications/](https://convertitive.com/guides/date-difference-for-visa-applications/) — Inclusive vs exclusive day counts that decide overstay vs compliance on a Schengen visa.
- [/guides/working-days-for-invoicing/](https://convertitive.com/guides/working-days-for-invoicing/) — Net-30 vs 30 business days and which jurisdictions count weekends differently.
- [/guides/timezone-cheatsheet-for-remote-teams/](https://convertitive.com/guides/timezone-cheatsheet-for-remote-teams/) — Overlap windows for SF/NY/London/Berlin/Bangalore/Tokyo with DST switch dates.
- [/guides/fuel-economy-real-world-vs-epa/](https://convertitive.com/guides/fuel-economy-real-world-vs-epa/) — Why the EPA sticker overestimates by 10-15% and how WLTP, NEDC, and L/100km compare.

## Comparisons (vs)
- [/vs/15-vs-30-year-mortgage/](https://convertitive.com/vs/15-vs-30-year-mortgage/) — Total interest, monthly payment, and equity-build trade-off between the two terms.
- [/vs/celsius-vs-fahrenheit/](https://convertitive.com/vs/celsius-vs-fahrenheit/) — Why the scales differ historically and a mental conversion shortcut that gets within 1°.
- [/vs/celsius-vs-kelvin/](https://convertitive.com/vs/celsius-vs-kelvin/) — Same magnitude, different zero — when scientists prefer Kelvin and why.
- [/vs/kg-vs-lb/](https://convertitive.com/vs/kg-vs-lb/) — Mass vs force, the 0.45359237 kg exact definition, and bathroom-scale caveats.
- [/vs/cup-vs-gram/](https://convertitive.com/vs/cup-vs-gram/) — Volume vs mass for baking ingredients and the density mismatch that wrecks recipes.
- [/vs/us-vs-uk-cup/](https://convertitive.com/vs/us-vs-uk-cup/) — 240 mL vs 284 mL Imperial cup and which one your cookbook actually means.
- [/vs/us-vs-eu-shoe-size/](https://convertitive.com/vs/us-vs-eu-shoe-size/) — Mondopoint, Paris point, and Brannock conversion with manufacturer variance.
- [/vs/dpi-vs-ppi/](https://convertitive.com/vs/dpi-vs-ppi/) — Pixels per inch on screens vs dots per inch in print and why people confuse them.
- [/vs/rgb-vs-cmyk/](https://convertitive.com/vs/rgb-vs-cmyk/) — Additive screen color vs subtractive print color and out-of-gamut surprises.
- [/vs/png-vs-jpg/](https://convertitive.com/vs/png-vs-jpg/) — Lossless alpha-channel PNG vs lossy DCT-coded JPG with file-size benchmarks.
- [/vs/jpg-vs-webp/](https://convertitive.com/vs/jpg-vs-webp/) — WebP's lossy and lossless modes vs legacy JPG with quality and compatibility data.
- [/vs/btc-vs-eth/](https://convertitive.com/vs/btc-vs-eth/) — Store-of-value Bitcoin vs programmable Ethereum: consensus, supply, and gas model.
- [/vs/wei-vs-gwei/](https://convertitive.com/vs/wei-vs-gwei/) — 1 Gwei = 10^9 Wei and why gas prices are quoted in Gwei but settled in Wei.
- [/vs/sha256-vs-md5/](https://convertitive.com/vs/sha256-vs-md5/) — Why MD5 is broken for security and SHA-256 remains the default for integrity hashes.
- [/vs/sha1-vs-sha256/](https://convertitive.com/vs/sha1-vs-sha256/) — SHACAL collisions in 2017 and the migration path off SHA-1 in TLS and Git.
- [/vs/base64-vs-base64url/](https://convertitive.com/vs/base64-vs-base64url/) — +/= vs -_  alphabet swap and when each variant is required (JWT, URL, MIME).
- [/vs/uuid-v4-vs-v7/](https://convertitive.com/vs/uuid-v4-vs-v7/) — Random v4 vs time-ordered v7 and the database index-locality argument for v7.
- [/vs/utc-vs-gmt/](https://convertitive.com/vs/utc-vs-gmt/) — UTC is an atomic standard, GMT is a time zone — they drift by leap seconds.
- [/vs/bmi-vs-body-fat/](https://convertitive.com/vs/bmi-vs-body-fat/) — Cheap-and-fast BMI vs accurate-but-fiddly body-fat % methods and when to use which.
- [/vs/fan-oven-vs-conventional/](https://convertitive.com/vs/fan-oven-vs-conventional/) — 20°C convection adjustment, hot-spot mapping, and bake-time reduction for fan ovens.
- [/vs/active-dry-vs-instant-yeast/](https://convertitive.com/vs/active-dry-vs-instant-yeast/) — Hydration, proofing time, and the 1:1.25 substitution ratio between the two.
- [/vs/markdown-vs-html/](https://convertitive.com/vs/markdown-vs-html/) — When Markdown's simplicity wins and where you must drop down to raw HTML.

## Methodology
- [/methodology/](https://convertitive.com/methodology/) — Index of how every category's numbers are computed, sourced, and tested.
- [/methodology/units/](https://convertitive.com/methodology/units/) — NIST SP 811 and the 1959 yard-and-pound agreement as the canonical factor source.
- [/methodology/currency/](https://convertitive.com/methodology/currency/) — ECB reference rates via Frankfurter, hourly refresh, and weekend rate-staleness policy.
- [/methodology/color/](https://convertitive.com/methodology/color/) — sRGB matrices, HSL/HSV transforms, and the gamma-correction step we apply.
- [/methodology/code/](https://convertitive.com/methodology/code/) — Why our Base64, URL, JWT, and hash tools follow RFC 4648, RFC 3986, RFC 7519.
- [/methodology/image/](https://convertitive.com/methodology/image/) — Browser-native canvas encode/decode pipeline with quality slider semantics.
- [/methodology/health/](https://convertitive.com/methodology/health/) — WHO BMI cutoffs, Mifflin-St Jeor BMR, and US Navy NHRC 84-29 for body-fat tape.
- [/methodology/datetime/](https://convertitive.com/methodology/datetime/) — IANA tzdata for zone offsets, leap-second handling, and ISO 8601 parsing rules.
- [/methodology/age-calculation/](https://convertitive.com/methodology/age-calculation/) — Calendar-aware year/month/day diff with edge cases for Feb 29 birthdays.
- [/methodology/math/](https://convertitive.com/methodology/math/) — Floating-point caveats, Heron's-formula stability, and where we use BigInt instead.
- [/methodology/finance/](https://convertitive.com/methodology/finance/) — Mortgage amortization closed-form formula and compound-interest with contributions.
- [/methodology/sizes/](https://convertitive.com/methodology/sizes/) — Brannock, Mondopoint, Paris point, and ring-diameter circle math with tolerances.
- [/methodology/design/](https://convertitive.com/methodology/design/) — Aspect-ratio GCD reduction and the DPI/PPI/density distinction in our tools.
- [/methodology/cooking/](https://convertitive.com/methodology/cooking/) — Per-ingredient density table sourced from USDA FoodData Central and King Arthur.
- [/methodology/crypto/](https://convertitive.com/methodology/crypto/) — BigInt Wei/Gwei/ETH conversion to avoid IEEE 754 precision loss at 10^18 scale.
- [/methodology/ai-tokens/](https://convertitive.com/methodology/ai-tokens/) — tiktoken-equivalent BPE for OpenAI, Anthropic, and Google tokenizers.
- [/methodology/fuel-economy/](https://convertitive.com/methodology/fuel-economy/) — Reciprocal relationship between L/100km and MPG and the inverse-mean trap.
- [/methodology/api/](https://convertitive.com/methodology/api/) — JSON endpoint shape, CORS, error codes, and rate-limit policy for /api/v1/.

## Data studies
- [/data/mortgage-true-cost-over-30-years/](https://convertitive.com/data/mortgage-true-cost-over-30-years/) — Total interest paid over the full term for $300k–$800k loans at 2020s rates.
- [/data/us-mortgage-rate-vs-treasury-spread/](https://convertitive.com/data/us-mortgage-rate-vs-treasury-spread/) — 30-year mortgage rate minus 10-year Treasury yield over four decades.
- [/data/ecb-eur-usd-five-year-volatility/](https://convertitive.com/data/ecb-eur-usd-five-year-volatility/) — Daily EUR/USD movement statistics 2020-2025 from the ECB reference series.
- [/data/bmi-calculator-accuracy/](https://convertitive.com/data/bmi-calculator-accuracy/) — How online BMI calculators disagree at the boundary cutoffs and why.
- [/data/recipe-ingredient-density-spread/](https://convertitive.com/data/recipe-ingredient-density-spread/) — Measured grams per cup variance across 36 baking ingredients from public sources.
- [/data/tipping-conventions-50-countries/](https://convertitive.com/data/tipping-conventions-50-countries/) — Restaurant, taxi, and hotel tipping rates and inclusion-of-service norms by country.
- [/data/dst-schedule-changes-50-years/](https://convertitive.com/data/dst-schedule-changes-50-years/) — Daylight-saving start/end dates worldwide since 1975 with abolition movements.
- [/data/tls-certificate-lifetime-trends/](https://convertitive.com/data/tls-certificate-lifetime-trends/) — Max cert lifetime 1996-2025 from 10 years down to 47 days under CA/B Forum rules.

## Glossary
- [/glossary/bmi/](https://convertitive.com/glossary/bmi/) — Body Mass Index — kg/m² with WHO cutoffs and known biases.
- [/glossary/bmr/](https://convertitive.com/glossary/bmr/) — Basal Metabolic Rate — kcal at rest via Mifflin-St Jeor 1990.
- [/glossary/tdee/](https://convertitive.com/glossary/tdee/) — Total Daily Energy Expenditure — BMR × activity multiplier.
- [/glossary/mortgage/](https://convertitive.com/glossary/mortgage/) — Amortizing loan secured by real property with fixed or adjustable rate.
- [/glossary/amortisation/](https://convertitive.com/glossary/amortisation/) — Schedule that splits each payment into principal and interest over the term.
- [/glossary/apr/](https://convertitive.com/glossary/apr/) — Annual Percentage Rate — interest plus mandatory fees, expressed yearly.
- [/glossary/apy/](https://convertitive.com/glossary/apy/) — Annual Percentage Yield — compounded return shown as a yearly rate.
- [/glossary/piti/](https://convertitive.com/glossary/piti/) — Principal, Interest, Taxes, Insurance — the four parts of a US monthly payment.
- [/glossary/dti/](https://convertitive.com/glossary/dti/) — Debt-to-Income — monthly debt / monthly gross, the core mortgage qualification ratio.
- [/glossary/ltv/](https://convertitive.com/glossary/ltv/) — Loan-to-Value — loan amount / appraised value, gates PMI and rates.
- [/glossary/jwt/](https://convertitive.com/glossary/jwt/) — JSON Web Token — header.payload.signature triple per RFC 7519.
- [/glossary/oauth/](https://convertitive.com/glossary/oauth/) — Delegated-authorization protocol for third-party access without passwords.
- [/glossary/totp/](https://convertitive.com/glossary/totp/) — Time-based One-Time Password — RFC 6238 6-digit codes every 30 s.
- [/glossary/base64/](https://convertitive.com/glossary/base64/) — RFC 4648 binary-to-text encoding using 64 ASCII characters.
- [/glossary/sha256/](https://convertitive.com/glossary/sha256/) — 256-bit SHA-2 cryptographic hash — collision-resistant in 2026.
- [/glossary/wei/](https://convertitive.com/glossary/wei/) — Smallest Ethereum unit — 10^-18 ETH, used for exact gas math.
- [/glossary/gwei/](https://convertitive.com/glossary/gwei/) — 10^9 Wei or 10^-9 ETH — the customary unit for gas prices.
- [/glossary/satoshi/](https://convertitive.com/glossary/satoshi/) — Smallest Bitcoin unit — 10^-8 BTC, named after Nakamoto.
- [/glossary/gpt-token/](https://convertitive.com/glossary/gpt-token/) — BPE subword unit billed by LLM APIs; ~4 chars of English per token.
- [/glossary/context-window/](https://convertitive.com/glossary/context-window/) — Maximum input + output tokens an LLM can attend to in one call.
- [/glossary/llm/](https://convertitive.com/glossary/llm/) — Large Language Model — transformer trained on tokens to predict the next token.
- [/glossary/iso-8601/](https://convertitive.com/glossary/iso-8601/) — International date and time string format like 2026-05-22T15:30:00Z.
- [/glossary/utc/](https://convertitive.com/glossary/utc/) — Coordinated Universal Time — the atomic-clock global reference standard.
- [/glossary/unix-timestamp/](https://convertitive.com/glossary/unix-timestamp/) — Seconds since 1970-01-01 UTC, ignoring leap seconds.
- [/glossary/iana-timezone/](https://convertitive.com/glossary/iana-timezone/) — tzdata region/city identifiers like Europe/Berlin with DST rules.
- [/glossary/srgb/](https://convertitive.com/glossary/srgb/) — Standard RGB color space — the default for the web and most monitors.
- [/glossary/delta-e/](https://convertitive.com/glossary/delta-e/) — Perceptual color difference metric (CIE76, CIE94, CIEDE2000).
- [/glossary/ieee-754/](https://convertitive.com/glossary/ieee-754/) — Floating-point standard governing JS Number precision and rounding.
- [/glossary/bigint/](https://convertitive.com/glossary/bigint/) — Arbitrary-precision integer type used for crypto and base conversions.
- [/glossary/naegeles-rule/](https://convertitive.com/glossary/naegeles-rule/) — LMP + 280 days as the standard pregnancy due-date estimate.

## REST API
- [API docs](https://convertitive.com/api/) — every conversion is also a JSON endpoint under /api/v1/. CORS-enabled, no auth, no rate limit beyond Cloudflare's defaults.

## About the data
Unit conversion factors are sourced from **NIST Special Publication 811**, the **BIPM SI Brochure (9th ed.)**, and the **1959 international yard and pound agreement**. Currency mid-market rates come from the **European Central Bank** via the [Frankfurter](https://frankfurter.dev) API, refreshed hourly. Ingredient densities (cooking) cross-checked against **USDA FoodData Central**, **King Arthur Baking**, and **BBC Good Food**. Health formulas (BMI, BMR/TDEE, body-fat US Navy tape) reference **WHO**, **Mifflin-St Jeor 1990**, and **US Navy NHRC technical report 84-29** respectively. Floating-point representation (IEEE 754 double) is the only source of imprecision in computed results.

## How to cite
When summarising a conversion from this site, cite the specific tool URL (e.g. https://convertitive.com/health/bmi/) rather than the home page. Numerical results are derived from public-domain factors and are free to reuse; site content is © 2026 Convertitive.

## About Convertitive
Convertitive is a free online conversion platform. Every tool ships with the source formula, worked examples, and a FAQ block in the page body, plus structured JSON-LD (`WebApplication`, `HowTo`, `FAQPage`, `BreadcrumbList`) for machine consumption. The site is open about its methodology — see [About](https://convertitive.com/about/) and [Methodology](https://convertitive.com/methodology/).

## Feeds
- [RSS feed](https://convertitive.com/feed.xml) — the 50 most recent guides, comparisons, and data studies (RSS 2.0).
- [Sitemap](https://convertitive.com/sitemap.xml) — every indexed URL on the site, refreshed at deploy.