Water Intake Calculator
Estimate how much water to drink daily based on your body weight and activity level.
Formula last reviewed 4 August 2026 · How we verify our calculators
Daily water (litres)
- In millilitres
- 2,450
- Glasses (250 ml)
- 10
Updates live as you type
Frequently asked questions
A common guideline is about 35 ml per kilogram of body weight. For a 70 kg adult that is roughly 2.45 litres, before adjusting for activity and climate.
Yes. Active and very active people lose more through sweat, so this calculator adds about 500 ml on top of the baseline. Hot weather increases needs further.
Partly. Foods with high water content and other fluids contribute to hydration, so you may not need to drink the full figure as plain water.
Rarely, but excessive intake in a short time can dilute blood sodium (hyponatraemia). Spread your intake through the day and listen to your thirst.
10 glasses, not 8 — and that's before you factor in a workout
Forget the generic "8 glasses a day" advice: a 70 kg adult at moderate activity needs closer to 2,450 ml — 2.45 litres, or about 10 glasses of 250 ml each — using the common 35 ml-per-kilogram guideline this calculator is built on. Push the same 70 kg into "active" or "very active" territory, and the target climbs by roughly 500 ml to account for sweat loss, landing near 2.95 litres. The generic 8-glass figure isn't wrong exactly, it's just weight-blind — this calculator isn't.
Why weight is the starting point, and activity is the adjustment
35 ml per kilogram of body weight is the baseline, scaling hydration need to body size rather than treating every adult identically. On top of that baseline, the calculator adds roughly 500 ml for active or very active activity levels specifically, since sustained exercise increases fluid loss through sweat well beyond what a sedentary day accounts for. The result is broken into litres, millilitres and 250 ml glasses — pick whichever unit is easiest to actually track through the day.
What can push your real number above this baseline
Hot or humid climates, intense or prolonged exercise sessions, illness — especially fever or diarrhoea — and pregnancy or breastfeeding can all raise fluid needs well past what this baseline captures, and none of those factors show up in the calculator's inputs. Food and other drinks count too: water-rich fruits, soups and beverages like tea contribute meaningfully to total hydration without needing to be tracked separately as "water." One practical real-world check worth pairing with any calculated number: urine colour. Pale straw generally signals good hydration; consistently dark urine is a sign to drink more, regardless of what any formula says. Use this target to build a consistent daily habit, not as a rigid number to hit precisely every single day.
This is a general estimate, not medical advice. Consult a doctor or registered dietitian for personalised guidance.