What to eat
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Hydration
Water Intake Calculator
A daily water target based on your body weight and exercise. Individual needs also vary with climate, diet, and health.
How much water you actually need
Daily fluid needs vary from person to person, but body weight and activity are the two biggest levers, and they're what this calculator uses. It applies roughly 33 millilitres of water per kilogram of body weight and adds about 350 millilitres for every 30 minutes of exercise. The result is a sensible baseline target rather than a strict prescription.
Importantly, your target includes all fluids, not just plain water. Tea, coffee, milk, and the water in food all count, and food alone can supply around a fifth of many people's daily fluid. That's why the number may look larger than the amount of water you actually pour into a glass.
Adjusting for real life
Hot or humid weather, altitude, illness with fever, pregnancy, breastfeeding, and hard training all raise your needs, sometimes substantially. On those days, drink more than the baseline. In cool weather with little activity, you'll naturally need less.
Rather than fixating on hitting an exact figure, use simple feedback: pale-yellow urine and only occasional thirst usually mean you're well hydrated. Sip through the day instead of drinking large amounts at once, and if you exercise hard or sweat heavily, consider replacing electrolytes as well as fluid. If you run or train regularly, our running pace calculator can help you plan sessions.
Per-kilogram estimates reflect common clinical guidance; total-fluid advice follows EFSA and U.S. National Academies reference intakes. Individual needs vary — this is an estimate only.
Frequently asked questions
How much water should I drink a day?
A common guide is about 30–35 ml per kilogram of body weight, plus extra for exercise. This calculator uses roughly 33 ml per kg and adds about 350 ml for every 30 minutes of activity. Health authorities also note that food and other drinks contribute to your total fluid.
Does coffee and tea count toward hydration?
Yes. Despite their reputation, moderate coffee and tea count toward daily fluid intake, and food contributes roughly 20% of the total for many people. The figure here is a target for total water; you do not need to drink all of it as plain water.
Can you drink too much water?
Rarely, but yes — drinking far more than you need in a short time can dilute blood sodium, a condition called hyponatremia. Spread intake through the day and let thirst and urine colour guide you rather than forcing large volumes at once.
How do I know if I am hydrated?
Pale-yellow urine and infrequent thirst are good everyday signs. Needs rise in hot weather, at altitude, during illness, and with hard exercise, so treat the number as a baseline to adjust upward when conditions demand.
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