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How much water is a reasonable daily target?
A baseline from body weight, plus what you sweat out. It is a planning figure, not a prescription.
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Where the baseline comes from
The baseline uses 35 millilitres of fluid per kilogram of body weight, a common population-level rule of thumb. Exercise adds roughly half a litre per 30 minutes, and hot weather adds more because sweat losses rise before thirst registers them.
Food contributes a meaningful share of total fluid intake, so the number is a ceiling for drinking, not a quota that must be met with a bottle.
When to ignore the number
Kidney, heart and liver conditions can require restricted fluid intake, and some medications change fluid balance. In those cases a clinician's target replaces any calculator. Urine colour is a better daily signal than a fixed number.
Frequently asked questions
Does coffee count?
Yes for most people. Moderate caffeine does not meaningfully increase fluid loss, and the drink still contributes water.
Is more always better?
No. Drinking far beyond need can dilute sodium. Spread intake across the day and let thirst do part of the work.
How much extra for hot weather?
The calculator adds 0.5 L for hot conditions and 1 L for very hot conditions. Actual sweat loss depends on humidity, work rate and clothing.
Does body weight include muscle and fat the same way?
No. The rule of thumb is crude; a lean, muscular person and a person with more body fat at the same weight may need different amounts. Use it as a starting point.