Water Intake Calculator

Water Intake Calculator estimates daily fluid needs from body weight, adds an allowance for exercise and adjusts for climate. The baseline is 35 millilitres per kilogram, the usual adult rule of thumb, which lands close to the published totals from both European and American health authorities for an average adult.

Two things are worth knowing about any figure like this. First, roughly a fifth of most people's fluid comes from food -- fruit, vegetables, soup, even bread -- so the amount to drink is less than the total. Second, everything you drink counts: tea, coffee, milk and juice are all mostly water, and the old claim that caffeine is so dehydrating as to cancel itself out does not hold at ordinary intakes.

For healthy adults, thirst is a reliable guide and these numbers are a sanity check rather than a quota. The exceptions are worth naming: older adults have a blunted thirst response, and anyone exercising hard in heat can lose fluid faster than thirst keeps up with. Drinking far beyond need is not harmless either -- it dilutes blood sodium, which in extreme cases is dangerous.

This is general information and not medical advice. The formula cannot know your medical history, your medication, your body composition or anything else specific to you. Speak to a doctor or another qualified professional about any question concerning your health, and never delay seeking advice because of a figure on this page.

Your measurements are processed inside your own browser. Height, weight, age and anything else you enter never leave your device, nothing is logged, and nothing survives closing the tab.

• Shows daily fluid, from body weight, for exercise and climate, glasses and typically from food together, so you are not running it twice
• A results table you can read across
• Updates as you type, with no button to press and no page reload
• Copy the result in one click
• Free, no sign-up, and it runs entirely in your browser

The water intake calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Getting a rough daily fluid target
• Adding an allowance for a long training session
• Adjusting intake for a hot climate or altitude
• Converting litres into glasses or bottles