EXAMPLE
A 70kg person with 30 minutes of exercise needs about 2.7 liters/day.
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How this calculator works
Daily water needs scale with body size and activity level. This calculator uses a common baseline of about 33 mL per kilogram of body weight, plus an additional amount for exercise, to estimate a daily fluid target.
THE MATH BEHIND IT
Base amount: weight (kg) × 0.033 L
Exercise addition: 0.35 L per 30 minutes of exercise
Daily target: Base + exercise addition
A real example
A person weighing 70 kg who exercises for 30 minutes:
Base amount
70 × 0.033 =2.31 L
Exercise addition
0.35 L
Daily target
2.31 + 0.35 =≈ 2.66 L
Common questions
It is a commonly cited general guideline (roughly 33 mL per kilogram of body weight) used by health organizations as a starting estimate for daily fluid needs from body size alone, before accounting for activity, climate, or individual health factors.
Fluid loss from exercise varies by duration and intensity rather than by body weight alone, so it is calculated separately and added to the base amount rather than folded into a single weight-based multiplier.
No — this estimate is based on body weight and exercise duration only. Hot weather, high altitude, and illness can all increase fluid needs beyond this baseline figure.