How the estimate is built
Two things drive how much fluid you need: your body size and how much you sweat. This calculator allows about 33 ml of water per kilogram of body weight as a baseline, then adds roughly 350 ml for every 30 minutes of exercise to replace what you lose through sweat.
The pie chart splits your total into the baseline need and the extra from activity, so you can see how much of your target comes from exercise.
What else changes your needs
The formula is a starting point. Several everyday factors raise or lower how much you should drink.
- Hot or humid weather and high altitude increase fluid loss.
- Fever, illness, pregnancy and breastfeeding raise needs.
- Fruit, vegetables and other foods supply water too, so drink needs may be a little lower.
- Caffeine and alcohol have a mild diuretic effect.
Listening to your body
Thirst and urine colour are simple, reliable guides. Pale straw-coloured urine usually means you are well hydrated, while dark urine suggests you should drink more.
Spread intake through the day rather than drinking a large amount at once, and drink a little extra around exercise.
A note on health
This is a general estimate, not medical advice. Drinking far more than you need can, in rare cases, dilute blood sodium dangerously. People with heart or kidney conditions may be given specific fluid limits, so follow your doctor’s guidance over any calculator.
Formula
water (ml) = weight·33 + (activity minutes / 30)·350Frequently asked questions
- Does this include water from food?
- No. The estimate is total fluid intake from drinks. Food (especially fruit and vegetables) also contributes water, so your needs from beverages may be a little lower.