Water Intake Calculator

Water keeps virtually every system in your body working — temperature regulation, circulation, digestion, and joint lubrication all depend on it. But how much any one person needs genuinely varies, which is why we're upfront that this number is a rough guide, not a rule.

The figure here uses a common clinical estimate of about 35 ml per kilogram of body weight. For context, the National Academies' Adequate Intake for total water — counting what comes from food as well as drink — is roughly 3.7 litres a day for men and 2.7 for women. Around 20% of most people's water comes from food.

The most reliable everyday guide isn't a formula at all: for most healthy adults, drinking to thirst and aiming for pale-yellow urine works well. Increase your intake when it's hot, when you exercise, and when you're unwell.

Estimate. We multiply your body weight in kilograms by about 35 ml, a commonly used clinical approximation of daily fluid needs, and show the result in litres.

Context. We also surface the NASEM total-water Adequate Intake (3.7 L men, 2.7 L women), which counts all sources including food — a useful sanity check on the weight-based figure.

Confidence. We label this estimate-only, and mean it: there is no validated personal formula for water needs, and individual variation is large. Use the number as a ballpark and let thirst do the fine-tuning.