Water Intake Calculator

There is no universal daily water target. Your needs depend on your body size, how active you are, the climate, your diet and your health. This calculator gives a practical personal estimate for your drinks, then shows the fixed authority baselines so you can sanity-check it against official guidance.

The personal figure starts from your body weight at about 33 ml per kg, the middle of the widely used 30 to 35 ml per kg rule of thumb for healthy adults. It then adds roughly 350 ml, about one large glass, for every 30 minutes of exercise, and increases the total by around 10% in a hot climate where you sweat more.

This estimate is for the fluids you drink. Because food provides water too, your drinking target can sit a little below the total-water baselines that include food.

For context, the tool shows two respected total-water adequate intakes. The European Food Safety Authority (EFSA) sets about 2.0 liters a day for women and 2.5 liters for men. The US National Academies (NASEM) set about 2.7 liters for women and 3.7 liters for men. Both figures are total water from drinks and food combined, which is why they are higher than a drinks-only estimate.

Any formula is a starting point, not a prescription. Two people of the same weight can need noticeably different amounts depending on sweat rate, muscle mass, medication and the day itself. Treat the number as a helpful daily aim, and adjust up when you are active or hot and down when you are not.

Some situations change your needs and are not covered by a general calculator: pregnancy and breastfeeding, kidney or heart conditions, certain medications, and illness with fever, vomiting or diarrhea. Drinking far too much too quickly can also be harmful by lowering blood sodium. If you have a medical condition or are unsure, follow advice from a health professional rather than a formula.

Use the liters, glasses, cups or ounces figure as a loose daily aim and spread it across the day rather than drinking it all at once. Let thirst and pale-yellow urine fine-tune it: drink more on hot or active days, less when you are cool and still. Everything is worked out in your browser, and you can switch between metric and imperial units at any time.