Water Intake Calculator
Calculate daily water intake based on weight, activity level, and climate.
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Quick Tip
Enter your body weight.
About This Tool
Why use Water Intake Calculator?
This calculator estimates daily fluid needs from body weight, exercise time and climate. The base figure is about 33 ml per kilogram of body weight, plus 500 ml for each hour of exercise, with the total raised 15% in hot conditions and lowered 5% in cold.
For a 70 kg person training for an hour in a temperate climate that is roughly 2.8 litres — about 11 glasses of 250 ml. Not all of it has to be plain water: tea, coffee, milk and the water in fruit and vegetables all count. Thirst and urine colour are still the best day-to-day guides, and people with kidney or heart conditions should follow the limits their doctor sets.
Key Benefits
Weight, exercise and climate together
Three factors that genuinely change fluid needs, rather than a fixed eight-glasses rule.
Four units shown
Litres, millilitres, US fluid ounces and glasses, so the target fits whatever you drink from.
A starting point, not a prescription
Individual needs vary with health, medication and diet; use the figure as guidance and adjust to how you feel.
How to use Water Intake Calculator
- 1
Enter your body weight.
- 2
Add the hours of exercise you expect on a typical day.
- 3
Pick the climate you are in: temperate, hot or cold.
- 4
Read the target in litres, millilitres, fluid ounces and 250 ml glasses, and spread it through the day.
Best use cases
Set a realistic daily water goal for your body size.
Plan fluid intake for a hot day or a long training session.
Convert a litre target into glasses or bottles you can count.
Check whether a hydration app's target is reasonable.
Water Intake Calculator FAQs
How much water should I drink a day?
Around 30–35 ml per kilogram of body weight for most adults, which is roughly 2.1–2.5 litres at 70 kg, plus extra for exercise and heat. Needs vary between people.
Do tea, coffee and food count?
Yes. Most drinks contribute to fluid intake, and food supplies roughly 20% of it. Caffeine has only a mild diuretic effect at normal intakes.
How can I tell if I am drinking enough?
Pale straw-coloured urine and infrequent thirst usually indicate adequate hydration. Dark urine, headaches and fatigue suggest drinking more.
Can you drink too much water?
Yes, though it is rare. Drinking far more than the kidneys can excrete — typically litres in a short time — can dilute blood sodium dangerously. Spread intake through the day rather than drinking a large amount at once.
Related Health Tools
More free health tools that work well alongside water intake calculator.