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.
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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.