Use this free water intake calculator to find how much water to drink each day in seconds. Enter your body weight in kilograms or pounds and your daily exercise, and the water intake calculator shows your daily target in liters, US fluid ounces, and cups instantly — no sign-up, no account, and no personal information needed. Your numbers are calculated in your browser and are not sent to us.
Contents: Formula · How to use · Examples · Tips · FAQ · Related tools · Sources
No sign-up required. This water intake calculator works in your browser, so the weight and exercise you enter are not stored or sent to us. The result is a general guide, not medical advice.
Water Intake Calculator Formula
This water intake calculator uses a common weight-based guide: about 35 milliliters of water per kilogram of body weight per day, plus extra water for exercise. Exercise adds about 500 milliliters per hour, because you lose fluid through sweat.
Daily water (liters) = Body weight in kg × 0.035 + Exercise hours × 0.5
If you enter pounds, the water intake calculator first converts them to kilograms by multiplying by 0.453592. For example, 70 kg with 30 minutes of exercise gives 70 × 0.035 = 2.45 liters, plus 0.5 × 0.5 = 0.25 liters, for a total of 2.70 liters per day. That is about 91.3 US fluid ounces, or about 11.4 cups. The result is an estimate for a healthy adult in normal conditions, not a medical prescription.
How to Use the Water Intake Calculator
Type your body weight into the first box, choose kilograms or pounds, and type how many minutes you exercise each day. Tap Calculate Water Intake to see your daily target in liters, fluid ounces, and cups. Use the unit that feels natural to you: visitors in the United States often use pounds and cups, while visitors in the United Kingdom and Canada often use kilograms and liters, and this water intake calculator shows both.
Spread the total through the day rather than drinking it all at once, and remember that food also contains water. Hot weather, illness, pregnancy, and intense training all increase needs, so use the result as a starting point and listen to your body.
Water Intake Calculator Examples
Example 1 — 70 kg, 30 minutes of exercise. 70 × 0.035 + 0.5 × 0.5 = 2.70 liters per day (about 91.3 fl oz, 11.4 cups).
Example 2 — 60 kg, no exercise. 60 × 0.035 = 2.10 liters per day (about 71.0 fl oz, 8.9 cups).
Example 3 — 154 lb (about 70 kg), 60 minutes of exercise. 154 × 0.453592 = 69.85 kg, then 69.85 × 0.035 + 1 × 0.5 = 2.94 liters per day (about 99.5 fl oz, 12.4 cups).
These water intake calculator examples show why a single “8 glasses a day” rule does not fit everyone: a heavier person and a person who exercises need more water than a lighter, inactive person.
Water Intake Calculator Tips
Carry a reusable bottle and refill it through the day, so the daily target feels manageable. Drink more in hot weather and during long workouts, and do not wait until you feel very thirsty. For general guidance on hydration, see Mayo Clinic's guide to how much water you should drink. If you have a health condition that affects fluid intake, such as kidney or heart disease, follow your doctor's advice instead of a general calculator.
Water Intake Calculator FAQ
What does a water intake calculator do? A water intake calculator estimates how much water you should drink each day from your body weight and exercise, and shows the result in liters, fluid ounces, and cups.
How much water should I drink per day? It depends on your weight and activity. As a guide, this water intake calculator uses 35 ml per kilogram of body weight, plus 500 ml per hour of exercise.
Can I enter pounds instead of kilograms? Yes. Choose Pounds (lb) and the water intake calculator converts your weight to kilograms before calculating.
Is 8 glasses a day correct? Eight glasses is about 1.9 liters, which is close for some adults but low for heavier or active people. A weight-based water intake calculator gives a more personal estimate.
Does food count toward water intake? Yes, food contains water, especially fruit, vegetables, and soups, so the calculator's total includes water from all sources, not only drinks.
Why does exercise raise the result? Because you lose fluid through sweat. This calculator adds about 500 ml per hour of exercise to the weight-based estimate.
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This calculator uses a common weight-based guide of about 35 ml of water per kilogram of body weight per day, plus about 500 ml per hour of exercise. Imperial entries are converted first (pounds x 0.453592). Results are estimates for general planning, not medical advice. Last updated: October 28, 2026.
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