Estimate your daily water needs from body weight, exercise and climate, in litres and in glasses.
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Water needs vary with body size, how much you sweat, and the temperature and humidity around you. A common planning figure is about 35 millilitres per kilogram of body weight per day, which covers an average adult at rest in a temperate climate.
The calculator adds water for each minute of exercise and an extra allowance for hot or humid conditions. Food also supplies water, often a fifth or more of the total, so the figure is best used as a target for drinks, not a precise prescription.
The eight-glass rule is a rough guideline, not a scientific requirement. Needs depend on body size and activity, and much of your intake comes from food and other drinks. Use your weight and activity to estimate, and watch your urine colour as a simple check.
Pale yellow urine usually means you are well hydrated. Dark yellow urine, infrequent urination, headache, or dizziness can signal you need more fluid. Thirst is a reliable signal for most healthy adults.
Yes, though it is rare. Drinking very large volumes quickly can lower blood sodium, which is dangerous. Spread intake through the day and seek advice if you have kidney, heart or liver conditions or take diuretics.
Yes, they contribute to fluid intake. Caffeine has only a mild diuretic effect at normal amounts, so moderate tea and coffee still count toward your daily total.
The calculator uses about 12 millilitres per minute of exercise, roughly 700 ml an hour. Heavy sweating in heat can need more, so weigh yourself before and after long sessions to judge your losses.
No. The calculation happens in your browser and nothing is saved.