Water Requirement Calculator
Estimate the water your body needs each day from your weight, exercise time and the climate.
Recent
Formula
How the calculation works
The base amount is your weight times 35 millilitres, a common rule of thumb.
Exercise adds 12 millilitres per minute, and the climate factor adjusts for hot or cold weather.
The result is given in millilitres, litres and standard glasses of 250 millilitres.
Common mistakes
- Drinking it all at once instead of spreading it through the day.
- Ignoring that tea, coffee and juicy fruit also add to daily fluid.
When to use it
- Use it to set a daily water target for your weight, activity and climate.
- It is not medical advice; heart or kidney conditions change fluid needs.
Worked example
A 70 kg person exercising 30 minutes in hot weather needs 2450 plus 360 ml, times 1.1, which is 3091 ml or about 12.4 glasses.
Common questions
How is the base amount calculated?
The base is 35 millilitres for every kilogram of body weight, which covers normal daily losses.
Why does hot weather increase the need?
Heat makes you sweat more, so the tool applies a 1.1 factor in hot weather and reduces it in cold weather.
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