Water intake
calculator
Eight glasses is folklore; body weight, training and climate are what actually move the number. Get a personalized daily estimate — and the honest context around it.
What the estimate is built on
The base is a widely used clinical heuristic of roughly 30–40 ml per kilogram of body weight per day (this tool uses 35). Exercise adds about 350 ml per half hour of sweating; hot, humid or very dry climates add more on top.
The honest science
There is no precise universal requirement — official references (like the US National Academies' ~3.7 L men / ~2.7 L women of total fluids) include the 20–30% that arrives in food, and coffee and tea count toward the total despite the caffeine myth. Thirst plus pale-yellow urine is a genuinely good regulator for most healthy people; the number above is a planning aid, not a prescription.
When needs genuinely rise
Heavy sweating, heat, altitude, illness, and pregnancy or breastfeeding all raise requirements. Overdoing it is possible too — forcing large volumes far beyond thirst serves no purpose and, in extremes, is dangerous. Training hard? Pair this with the TDEE calculator for the fuel side.
Water intake FAQ
A common clinical estimate is 30–40 ml per kg of body weight — about 2.7 L for a 78 kg person before exercise. Official total-fluid references are ~3.7 L for men and ~2.7 L for women, including the fluid in food.
Yes. Despite the old myth, caffeinated drinks contribute net fluid at normal intakes. Food also supplies roughly 20–30% of total water for most people.
It has no clear scientific origin. Needs vary with body size, activity and climate — which is exactly what this calculator adjusts for. Thirst and pale-yellow urine are better everyday guides.
Yes — drinking far beyond thirst, especially rapidly during endurance events without electrolytes, can dangerously dilute blood sodium (hyponatremia). More is not automatically better.