About this water intake calculator
A rough daily water target from your body weight and how active you are. Enter the weight in kilograms or pounds and the result comes back four ways — litres, 250 ml glasses, fluid ounces and 8 oz cups — so you can read whichever you actually think in. The baseline is about 35 ml per kilogram, scaled slightly for activity. Treat it as a starting point and nothing firmer: real need shifts with climate, what you eat, what else you drink and your health, none of which a weight can tell you.
How the water intake calculator works
Baseline intake is 35 ml for each kilogram of body weight. That is multiplied by 1.0 for sedentary, 1.1 for moderate and 1.2 for active, then expressed in litres, 250 ml glasses, US fluid ounces and 8 oz cups. A weight entered in pounds is converted to kilograms first, so both units give the same answer. The 35 ml per kilogram figure is a commonly cited rule of thumb, not a clinical guideline. It is useful because it scales with body size, which "eight glasses a day" does not.
Water Intake Calculator examples
70 kg, moderate activity
2.70 litres · about 10.8 glasses · about 91 fl oz · about 11.4 cups
150 lb, sedentary
About 81 fl oz · about 10.1 cups · 2.38 litres
60 kg, sedentary
2.10 litres · about 8.4 glasses
The same weight in kg or lb
Identical results — pounds are converted before the formula runs
Limitations & privacy
A general estimate, not medical advice, and not a target to hit precisely. It does not account for climate, exercise beyond the three activity bands, pregnancy, breastfeeding, illness, or any medical condition that changes fluid needs. People with kidney, heart or liver conditions should follow a clinician's specific guidance, which may be to drink considerably less than a figure like this. The number counts total fluid, not glasses of plain water. Food contributes a meaningful share — often around a fifth — and so does everything else you drink.
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Water Intake Calculator: frequently asked questions
How much water should I drink a day?
This gives roughly 35 ml per kilogram of body weight, adjusted for activity — about 2.7 litres or 91 fl oz for a moderately active 70 kg adult. It is a starting point. Thirst, climate and what else you eat and drink matter more than hitting a number exactly.
Is it really eight glasses a day?
That rule is widely repeated and has little behind it. It does not scale with body size, activity or climate, and it ignores the fluid in food and other drinks. A figure based on your weight is a better starting point, which is not the same as being precise.
Does this count water from food and other drinks?
The total is all fluid, not plain water alone. Food typically provides around a fifth of it, and tea, coffee, milk and soft drinks all count toward the rest. So the figure here is not the amount you need to drink from a glass.
Can I enter my weight in pounds?
Yes. Switch Units to Imperial. Pounds are converted to kilograms before the formula runs, so both give the same result, and the answer is shown in ounces and cups as well as litres.
Why does activity level matter?
More activity means more fluid lost through sweat and breathing. The three bands apply a modest adjustment — 10% for moderate, 20% for active — which is a rough stand-in for a range that varies far more than that in practice.
Is more water always better?
No. Drinking far more than you need can dilute blood sodium, which in extreme cases is dangerous. It also matters for anyone on a fluid restriction, where a figure like this could be actively wrong. If you have been told to limit fluids, follow that advice rather than this.
Updated October 19, 2026