How much water should you actually drink?
Calculate your recommended daily water intake based on your weight, exercise, climate, and caffeine habits.
How the math works
The baseline is the European Food Safety Authority's recommendation of roughly 30ml per kilogram of body weight. On top of that, the ACSM recommends an additional ~500ml per hour of exercise, WHO guidelines for hot/humid climates add ~500ml/day, and Mayo Clinic guidance suggests roughly 100ml extra per caffeinated serving to offset caffeine's mild diuretic effect. These factors stack additively — someone who exercises, lives somewhere hot, and drinks coffee applies all three on top of the weight-based baseline, since each addresses a genuinely separate source of fluid need.
A generic "8 glasses a day" rule doesn't account for any of this — the weight-based, factor-adjusted approach is more individualized.
Where this doesn't apply
- Individual sweat rates and hydration needs vary — these are general guideline-based adjustments, not personal measurements.
- Certain medical conditions (kidney, heart) require different fluid guidance than general population recommendations.
- This models direct beverage intake only — food also contributes meaningfully to total fluid intake.