Water Intake Calculator
Get a personalised daily fluid target that factors in your activity, climate, caffeine and alcohol — split into water from food and water from drinks.
How the calculation works
Baseline: ~35 ml of water per kg of body weight (Geneva Foundation guidance), adjusted down to 30 ml/kg over age 55 and up to 40 ml/kg under 18. Female baseline is set ~2 ml/kg lower to reflect average lean mass differences.
Exercise adds ~12 ml per minute of moderate activity. Climate adds 0–900 ml depending on heat exposure. Pregnancy adds 300 ml, breastfeeding adds 700 ml (IOM 2005).
Caffeine and alcohol are mild diuretics — we add small compensation (~80 ml per cup of coffee, ~250 ml per alcohol unit) to offset extra fluid loss.
