Daily Water Intake Calculator
Estimate how much water to drink each day from your body weight plus a top-up for exercise, shown in litres, millilitres and 8-ounce cups.
How it works
water (mL) = weight(kg)·33 + (exercise min ÷ 30)·350 + hot-climate top-up (10%)
A common rule of thumb sets baseline fluid needs at about 30–35 mL per kilogram of body weight, which this calculator applies at 33 mL/kg. On top of that, exercise adds fluid to replace what you lose through sweat and breathing — roughly 350 mL per half hour of activity — and hot or humid conditions raise needs further. Remember this is total fluid: water in food, tea, coffee and other drinks all count, so the plain-water amount you actually need to sip is lower.
Worked example
A 70 kg person doing 30 minutes of exercise in a temperate climate: base = 70·33 = 2,310 mL, plus (30 ÷ 30)·350 = 350 mL, for about 2,660 mL — roughly 2.7 litres or 11 cups of total fluid.
Sources: U.S. National Academies — Dietary Reference Intakes for water
Frequently asked questions
Do coffee and tea count toward my water intake?
Yes. Despite a mild diuretic effect, caffeinated drinks still provide a net gain of fluid, and the water in food adds a meaningful amount too. The target here is total daily fluid, not plain water alone.
Is the "8 glasses a day" rule right?
It is a rough average that happens to land near many people's needs, but it ignores body size, activity and climate. Scaling to weight and adding for exercise, as here, personalizes it better.
Can I drink too much water?
Rarely, but yes — drinking far more than you lose can dilute blood sodium (hyponatremia), which is dangerous. Use thirst and pale-yellow urine as guides and do not force large volumes well beyond the estimate.
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Educational estimate, not medical advice — for personal health decisions consult a qualified healthcare professional.