WATER BY WEIGHT
CALCULATOR
Simple weight-based water calculator — enter your weight, get your target.
Your Weight
Your Water Target
--
Litres / Day
Standard (35ml/kg)--
Active Adjusted (40ml/kg)--
Lean Mass Based--
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Hydration Reference
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Weight-Based Water Formula
The simplest evidence-based hydration guideline: drink approximately 30–35ml of water per kilogram of body weight per day. A 70kg person needs approximately 2.1–2.45L daily at baseline, before accounting for exercise or heat. This method is more accurate than blanket recommendations because it scales with body size.
Frequently Asked Questions
How much water per kg of body weight?
General guidance is 30–35ml per kg of body weight per day as a baseline. Increase to 40ml/kg on active days or in hot climates. For example, a 70kg person needs 2.1–2.45L at baseline, adding 500–750ml on exercise days.
Do larger people need more water?
Yes. Larger bodies have more cells requiring hydration and typically have higher metabolic rates, generating more metabolic water loss. Weight-based formulas are more accurate than fixed-quantity recommendations for this reason.