Daily water intake calculator
How much water you need depends mainly on your body size, how much you exercise and the weather. FitCalcs sets a baseline of about 33 ml per kilogram of body weight, which lands near the EFSA adequate-intake figures of roughly 2 litres a day for women and 2.5 for men, then adds for exercise and hot days. About a fifth of your fluid comes from food, and pale-yellow urine is still the best day-to-day guide. This is general information, not medical advice.
How this is worked out
FitCalcs sets a baseline from body weight, then adds for exercise and hot weather:
baseline ml = weight kg x 33
exercise top-up = 350 ml per 30 min of activity
total x 1.15 on a hot or humid day
The 33 ml per kg baseline lands near the EFSA adequate-intake figures (about 2.0 litres a day for women and 2.5 for men, from all drinks and food). Food provides roughly a fifth of your fluid, and thirst plus pale-yellow urine are still the best day-to-day guides.
Informational only, not medical advice. Some conditions need fluid limits set by a doctor. Editorially reviewed by FitCalcs, with each figure citing its source.
Calculators and Data Desk, FitCalcs
FitCalcs' editorial desk builds and documents the calculators, citing the underlying equation and the UK dataset behind every number. Health-related tools are editorially reviewed, with figures cited to named UK sources.
Last reviewed: 12 June 2026