Water Intake Calculator
Free water intake calculator: estimate how much water to drink per day from your body weight and exercise, in litres, ml, cups and bottles.
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- ✓ Free, no limits
~35 ml per kg + ~350 ml per 30 min of exercise. Food covers ~20% of daily fluid; thirst and pale-yellow urine remain the best gauge. An estimate, not medical advice.
This calculator estimates how much water to drink in a day from the two things that actually move the number: your body weight and how much you exercise. It uses the common ~35 ml per kilogram baseline and adds roughly 350 ml for every half hour of activity, then shows the result in litres, millilitres, US cups and standard 500 ml bottles.
Worked example: at 70 kg with no exercise the estimate is about 2.5 litres a day — five bottles; add an hour of training and it rises to about 3.2 litres. That lines up with the EFSA's general adequate-intake guidance of 2.0 litres for women and 2.5 for men from all sources.
Two honest notes: food typically contributes around a fifth of your fluid intake, so the drinking target is lower than the total; and thirst plus pale-yellow urine remain the best day-to-day gauge. Heat, altitude, pregnancy and some medical conditions change needs — this is a rule-of-thumb estimate, not medical advice. Nothing you enter is uploaded.
Frequently asked questions
How much water should I drink a day?
A reasonable estimate is ~35 ml per kg of body weight, plus ~350 ml per 30 minutes of exercise: about 2.5 L for a 70 kg adult. General guidance (EFSA) is around 2.0–2.5 L per day from all sources.
Is the '8 glasses a day' rule true?
It's a rough simplification — eight 250 ml glasses is 2 litres, close to guidance for many adults but blind to body size and activity. Weight-based estimates like this one adapt to you.
Does coffee or tea count toward my intake?
Yes. Despite the myth, caffeinated drinks hydrate on net, and food contributes roughly 20% of daily fluid on typical diets. Water is simply the zero-calorie way to get there.
Can I drink too much water?
Yes — drinking litres in a short window can dilute blood sodium (hyponatremia), which is dangerous. Spread intake across the day and let thirst lead; this tool is an estimate, not medical advice.