Water Intake Calculator
A rule-of-thumb estimate of daily fluid from weight, exercise and climate.
How it works
Enter your weight and the total minutes you exercise on a typical day, then pick the climate. The calculator adds the three parts together and shows the total in litres, with millilitres, US fluid ounces and US cups alongside.
base = 33 ml × weight (kg)
exercise = 350 ml × minutes ÷ 30
climate = +0 (cool or temperate), +250 ml (warm), +500 ml (hot or humid)
total = base + exercise + climate; range = total ± 10%Example
70 kg, 30 minutes of exercise, temperate climate: base = 33 × 70 = 2,310 ml; exercise = 350 ml; climate = 0. Total = 2,660 ml, shown as about 2.7 L, with a range of 2.4 to 2.9 L.
Common mistakes
- Treating the total as a target to hit with plain water. Food and other drinks count towards it.
- Forgetting that the exercise figure is for the day's total minutes, not for a single session.
- Ignoring medical advice. Some health conditions and medications change how much fluid is right for you.
Results are estimates and are not a substitute for medical advice.
About this calculator
This calculator uses a common rule of thumb: about 33 ml of fluid per kg of body weight per day, plus about 350 ml for every 30 minutes of exercise, plus 250 ml in warm weather or 500 ml in hot or humid weather.
The result is shown as an approximate figure with a range of 10% either side. It is not a requirement. Food and other drinks count, and real needs vary with health, medication, pregnancy and more. Talk to a clinician for medical guidance.
Frequently asked questions
How does the calculator work out the number?
It adds three parts: 33 ml per kg of body weight, about 350 ml per 30 minutes of exercise, and 250 ml (warm) or 500 ml (hot or humid) for climate. For 70 kg and 30 minutes of exercise in a temperate climate, that is 2,310 + 350 = 2,660 ml.
Is this how much water I must drink?
No. It is an approximate figure from a rule of thumb, shown with a range of ±10%. Your own needs may be higher or lower.
Does coffee, tea or food count?
Yes. Food and other drinks contribute to your fluid intake, so the total does not all have to come from plain water.
Which cup size is used?
US customary: 1 cup = 8 US fluid ounces, or about 236.6 ml. A US fluid ounce is about 29.6 ml.