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.
RM
Built by Ren Martin
Sports coach · 20+ years in fitness · Used this calculator personally
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.
Does body weight alone determine water needs?
Body weight is the best single predictor of baseline water requirements, but activity level and climate significantly modify individual needs. A 70kg sedentary person in a cool office needs approximately 2.1–2.5 litres per day. The same person doing 90 minutes of exercise in summer heat may need 3.5–4.5 litres. This calculator provides the bodyweight baseline — add approximately 500ml per 30 minutes of exercise.
Is sparkling water as hydrating as still water?
Yes. Carbonated water hydrates equally effectively as still water. The carbon dioxide in sparkling water is absorbed and exhaled — it does not affect fluid absorption or kidney function. The only meaningful difference is that carbonation can increase satiety and may cause bloating in some people, which can reduce total intake if drinking large volumes.
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.