Daily water intake calculator
Fluid needs scale with body mass and with how much you sweat. The eight-glasses rule has no evidence behind it; body weight at least has a mechanism.
minutes
Daily fluid target
2.84L
- In US cups
- 12.0
- In US fluid ounces
- 96
- Extra for exercise
- 525 mL
Show the working
- Body weight = 70
- Exercise per day = 45
- Climate = 1
- base_ml = 70 * 33 = 2310
- Extra for exercise = 45 / 30 * 350 = 525
- total_ml = (2310 + 525) * 1 = 2835
- Daily fluid target = 2835 / 1000 = 2.835
- In US cups = 2835 / 236.5882365 = 11.9828
- In US fluid ounces = 2835 / 29.5735295625 = 95.8628
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- base = 33 mL per kilogram of body weight
- exercise = 350 mL per 30 minutes
- total = (base + exercise) x climate factor
This counts all fluid, including what is in food, tea and coffee. Caffeine at normal doses is not meaningfully dehydrating.
Drinking far beyond thirst is not harmless; hyponatraemia is a real risk in endurance events.
This is a population formula, not a diagnosis. Individual metabolism, body composition and medical history all move the real answer, so treat the number as a starting point and talk to a clinician about anything that matters.