Water intake calculator
Daily water from weight and activity.
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How it's calculated
The common rule is half an ounce of water per pound of body weight a day, about 33 ml per kilogram, which lands near the 2.7 to 3.7 litres of total water the US National Academies suggest once food is counted. Add 12 oz (350 ml) for every 30 minutes of exercise, and about 16 oz (500 ml) more in hot or humid weather. The result is total fluid: coffee, tea, milk and the water in fruit and vegetables all count.
Is eight glasses a day right?
It is a reasonable floor for a small, inactive adult and low for most others. Eight 8-oz glasses is 64 oz; the weight rule gives 80 oz for a 160 lb person before exercise. The best guide is simpler: drink when thirsty and aim for pale yellow urine.
Does coffee count toward water intake?
Yes. Caffeine is a mild diuretic, but a cup of coffee still leaves you with more water than you lose. Alcohol is the exception: it dehydrates on balance.
Can I drink too much water?
Yes, though it takes effort: more than about a litre an hour for several hours, especially during long endurance events, can dilute blood sodium (hyponatraemia). Spread intake through the day and salt your food if you sweat a lot.
Results are estimates for informational purposes only and are not financial, medical or legal advice.