A weight-based daily water range, with an activity bump — a starting point, not a prescription.
There is no single “correct” number of glasses everyone should drink. Fluid needs depend on body size, activity, climate, diet, illness, pregnancy and breastfeeding, and a meaningful share of your daily water comes from food — roughly 20–30% for a typical diet. The calculator below uses the widely cited 30–35 ml per kilogram of body weight as a base band and adds about 12 ml per minute of exercise. Treat the output as a rough starting point and let thirst be your main guide. For authoritative population figures, see the EFSA and U.S. National Academies adequate-intake values cited below.
≈ 71–83 US fl oz / day
General estimate only (30–35 ml/kg, plus ~12 ml per minute of exercise). This is not a medical target — fluid needs vary with climate, diet, health, and pregnancy, and much of your daily water comes from food. Drink to thirst and ask a clinician about your own needs.
Type your weight in kilograms. The base estimate is 30–35 ml of water per kg, so a 70 kg adult lands around 2.1–2.45 litres per day before activity.
Enter minutes of exercise to add roughly 12 ml per minute — about 360 ml for a 30-minute session — split across the low and high bounds. Leave it at 0 on rest days.
The result is a band in litres and US fluid ounces. Aim somewhere inside it, drink more in heat or when sweating heavily, and remember food and other drinks count toward the total.
Base range only (no exercise), using 30–35 ml/kg. These are general estimates, not targets to hit precisely.
| Body weight | Base range (litres/day) | ≈ US fl oz/day |
|---|---|---|
| 50 kg | 1.5–1.75 | 51–59 |
| 60 kg | 1.8–2.1 | 61–71 |
| 70 kg | 2.1–2.45 | 71–83 |
| 80 kg | 2.4–2.8 | 81–95 |
| 90 kg | 2.7–3.15 | 91–107 |
Add ~0.36 L for every 30 minutes of exercise. A hot, humid day or heavy sweating can push real needs well above the high bound.
The per-kilogram rule is a clinical and sports-nutrition rule of thumb for estimating baseline fluid needs in healthy adults; it scales intake with body size, which a flat “2 litres for everyone” figure does not. It is an estimate, not a measured requirement — the authoritative population values come from EFSA and the U.S. National Academies, both cited below.
Fever, vomiting, diarrhoea, intense heat, high altitude, pregnancy and breastfeeding all raise fluid needs, while some heart, kidney, and liver conditions require deliberately limiting fluids. In any of these cases follow medical advice rather than a general calculator.
Authoritative references behind the math, constants, and tables on this page. Verified by Buğra Sözeri on the dates shown and re-checked at every deploy.