Water Intake by Body Weight Calculator
Estimate a daily water target from your body weight, with an add-on for exercise — in liters, ounces and cups.
How it works
Base = weight(kg) × 33 mL · Exercise add-on = (minutes ÷ 30) × 350 mL · Target = base + add-on
A common rule of thumb sets daily fluid at roughly 30–35 mL per kilogram of body weight, which scales intake to body size better than a flat "8 glasses" figure. Exercise adds losses through sweat, so this tool tacks on about 350 mL for every half hour of activity. Food, climate, altitude and health conditions all shift the real number, so treat the result as a starting target and let thirst and urine colour fine-tune it.
Worked example
A 160 lb person is 160 ÷ 2.205 = 72.6 kg. Base fluid is 72.6 × 33 = 2,395 mL. Thirty minutes of exercise adds (30 ÷ 30) × 350 = 350 mL, for a target of about 2,745 mL, or 2.75 L (roughly 93 oz).
Frequently asked questions
Does all of this have to be plain water?
No. Total fluid includes water, milk, tea, coffee and the water in foods like fruit and soup. Plain water is the simplest way to top up, but it does not all have to come from the tap.
Is more water always better?
No. Drinking far beyond your needs does not add benefit and, in rare cases of extreme overhydration, can dangerously dilute blood sodium. Use the target as a guide and drink to thirst rather than forcing large excesses.
How do I know if I am drinking enough?
Pale-yellow urine and infrequent thirst are practical signs of good hydration. Dark urine, headaches or persistent thirst suggest you should drink more.
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Educational estimate only — not medical advice, diagnosis, or treatment. Individual needs vary; consult a qualified healthcare professional for decisions about hydration, nutrition, medication, or substance use.