DPI vs PPI: the difference that costs designers money

TL;DR.PPI (pixels per inch) describes the resolution of an image at a target print size; DPI (dots per inch) describes the physical output resolution of a printer or scanner. Photoshop’s “DPI” setting is actually PPI. The terms are conflated everywhere but they are not the same.

DPI (dots per inch) and PPI(pixels per inch) are routinely used interchangeably. They aren’t the same thing. PPI describes an image; DPI describes a physical device. Confusing them is the most common reason print jobs come back blurry.

The two definitions

A 3000×2000-pixel image is just a 3000×2000-pixel image. It has no inherent DPI — it has dimensions in pixels. When you say it’s “300 PPI,” you’re asserting the target print size: 3000 ÷ 300 = 10 inches wide. The same file at 150 PPI prints 20 inches wide, at half the density.

Why Photoshop calls it DPI

Photoshop’s Image Size dialog has a field labelled “Resolution” with units of “pixels per inch” — which is PPI. But everyone, including Adobe’s own documentation in places, calls this setting “DPI.” The misuse is so ingrained that printers and designers communicate in DPI even when both mean PPI.

Translation key for everyday work: when someone says “send me the file at 300 DPI,” they mean 300 PPI at the intended print size. Make sure the pixel count matches: a 4×6 inch print at 300 PPI needs 1200×1800 pixels.

The math of print quality

Standard rules of thumb for what PPI you need:

• 72-96 PPI — web display. Browsers ignore the embedded PPI value; only pixel count matters.
• 150 PPI — newspaper print, large-format posters viewed from distance.
• 300 PPI — magazine/book print, photo prints, anything viewed at arm’s length.
• 600+ PPI — line art, technical drawings, fine type.

The PPI a printer can resolve is bounded by its actual DPI — but it’s not the same number. Inkjet printers typically run 1200-4800 DPI but the effective image resolution (PPI) they can reproduce is around 300, because producing one image pixel requires multiple ink dots (halftone screening).

Where the confusion bites

The classic failure: someone designs a print piece in Illustrator at 72 PPI (the screen default), exports a PDF, and sends it to a press. The press receives a file that says “72 PPI” in its metadata; the pixel content prints at 1/4 the intended density. The output looks soft, blocky, or pixelated.

Fix: re-export at 300 PPI andensure the source images contain enough pixels to support that density at the final print size. A 100×100-pixel logo cannot be printed sharply at 4 inches square — there’s simply not enough information regardless of the PPI value embedded in the file.

Web vs print: when PPI matters

For the web, embedded PPI is mostly cosmetic. Browsers display images using their pixel count, not their PPI metadata. A 1000×1000 image looks identical at 72 PPI and 300 PPI in Chrome.

The exception is “Retina” / high-DPI displays. Modern devices have 2-3× the physical pixel density of the old CSS pixel. Designers serve @2x or@3xassets with double or triple the pixel count of the CSS dimensions. The embedded PPI metadata still doesn’t matter — only the pixel count does.

The takeaway

Talk in pixels when the medium is digital. Talk in PPI at a target print size when the medium is print. Use “DPI” only when you literally mean the printer or scanner’s hardware resolution.

For colour conversion math (which has its own pitfalls), see our colour methodology page.

Numeric facts

• 1 inch = 25.4 mm exactly, so 300 PPI = 11.811 pixels/mm; 1 PPI = 0.03937 px/mm.
• 72 PPI legacy: the original Mac “1 point = 1 pixel = 1/72 inch” convention; baked into PostScript and PDF, irrelevant on modern displays.
• Apple Retina (iPhone 15 Pro): 460 PPI; iPad Pro 264 PPI; MacBook Pro 14" Liquid Retina XDR 254 PPI.
• 4×6 inch photo print at 300 PPI needs 1200 × 1800 px; at 150 PPI, 600 × 900 px is sufficient (poster viewing distance).
• Inkjet hardware DPI: 1200-4800 dots/inch; effective image resolution (PPI it can render) is ~300 because halftoning consumes 4-16 ink dots per image pixel.
• Offset press LPI (lines per inch, the actual halftone screen): 133 LPI newspaper, 150 LPI magazine, 200 LPI fine art — and rule of thumb says PPI ≥ 2 × LPI for sharp output.
• Visual acuity threshold: a 20/20-vision human resolves about 1 arcminute, which at 30 cm viewing distance equals ~290 PPI — the basis for the “Retina” threshold.
• CSS pixel ratio: standard display = 1, Retina = 2, recent Android flagships = 2.625 or 3. Browser devicePixelRatio exposes the value.

Decision matrix

Sources

• Adobe — Photoshop User Guide: Image size and resolution — helpx.adobe.com.
• ISO 12640-2 — Prepress digital data exchange, defines image resolution requirements for offset print — iso.org.