Daily Water Intake Calculator
Estimate how much water to drink a day based on weight, activity and climate.
Recommended Hydration Target
How much water you need isn't a single fixed number — it rises with body weight, exercise, and heat. This calculator estimates a sensible daily target from your age, sex, weight, activity level, and climate, and expresses it three ways: ounces, standard 8-ounce glasses, and litres. For children it falls back to age-based guidance. Everything is worked out in your browser, and nothing you enter is saved.
How the estimate is built
For teenagers and adults, the calculator starts from body weight, then adds for how active you are and whether you live somewhere hot:
Base (oz) = Weight in lb × 0.67 (men) or × 0.5 (women), then + activity + climate
Activity adds between 6 and 32 ounces depending on how hard you train, and a tropical climate adds a further 12 ounces. A 160-pound man who exercises moderately would land around 119 ounces, or roughly 15 glasses. For children under 14 the tool uses established age-band recommendations instead, since weight-based formulas aren't appropriate for growing bodies.
What counts and what to watch
Your target includes all fluids, not just plain water — food, especially fruit and vegetables, typically supplies a fair share too, so you don't need to drink the entire figure from a glass. Thirst and urine colour are good everyday guides. The numbers here are a general estimate; needs rise with illness, pregnancy, breastfeeding, and certain medications, and some heart or kidney conditions require fluid limits. Drinking far beyond your needs isn't beneficial and, in rare cases, can be harmful.
Frequently Asked Questions
Does this include water from food and other drinks?
The target represents your total daily fluid needs, and food and other beverages contribute to it. You generally don't need to drink the whole amount as plain water — a portion comes from what you eat.
Why does activity and climate raise the number?
Because you lose fluid through sweat. Harder exercise and hot or tropical climates increase those losses, so the calculator adds a set amount to cover them.
Is this medical advice?
No. It is a general educational estimate, not medical advice. Needs change with pregnancy, illness, and certain conditions, and some people are advised to limit fluids — check with a doctor if you have specific health concerns.
Is my information saved?
No. The calculation runs in your browser and nothing you enter is uploaded or stored.