How much water should I drink per kg of body weight?

A common guideline is about 30 to 35 ml of water per kilogram of body weight per day. This calculator uses roughly 33 ml per kg, then adds an allowance for moderate or intense exercise.

How many litres should a 70 kg person drink?

At 33 ml per kg, a 70 kg adult has a baseline of about 2.3 litres per day. With moderate exercise that rises to roughly 2.8 litres, and with intense exercise to about 3.3 litres.

Does exercise change how much I should drink?

Yes. Exercise increases fluid loss through sweat, so the calculator adds about half a litre for moderate activity and a full litre for intense activity on top of the baseline.

Does food count towards my water intake?

Yes. Roughly 20 percent of daily fluid typically comes from food, especially fruit and vegetables. This calculator estimates total water needs, so part of that target can be met through what you eat as well as what you drink.

Can I enter my weight in pounds?

Yes. Choose pounds and the calculator converts to kilograms internally (1 lb is about 0.4536 kg) before applying the 33 ml per kg guideline, so the result stays accurate.

Can I drink too much water?

Yes. Drinking very large amounts in a short time can dilute blood sodium (hyponatraemia), which is dangerous. Treat this figure as a daily guide spread across the day, not a target to hit quickly, and follow medical advice if you have a heart or kidney condition.

Is anything uploaded?

No. The calculation happens entirely in your browser and nothing is sent anywhere.

Water Intake by Body Weight Calculator

How much water should you drink?

This calculator estimates your recommended daily water intake from your body weight and activity level. Hydration needs scale with body mass, so a weight-based estimate is a practical starting point for most healthy adults — more reliable than the one-size-fits-all “eight glasses a day” rule.

How it works

The tool converts your weight to kilograms if needed, then applies a common hydration guideline of about 33 ml of water per kilogram of body weight, and adds a fixed allowance for exercise:

daily water (litres) = (weight in kg × 33 ÷ 1000) + activity allowance

The activity allowance is 0 litres for low/sedentary, 0.5 litres for moderate exercise, and 1.0 litre for high/intense exercise. The result is shown in litres, then converted to 250 ml cups and US fluid ounces (1 litre ≈ 33.814 US fl oz).

Activity level	Added allowance
Low / sedentary	0 L
Moderate exercise	+0.5 L
High / intense exercise	+1.0 L

Example

A 70 kg adult with moderate activity: baseline = 70 × 33 ÷ 1000 = 2.31 L, plus 0.5 L for exercise = 2.81 litres per day. That is about 11 cups (250 ml each) or roughly 95 US fl oz.

Your real needs also depend on climate, diet, illness and medical advice, so use this as a starting point. Everything is calculated in your browser — nothing is uploaded.