Water Intake Calculator
How it works
The baseline is a commonly cited 33 ml of water per kilogram of body weight. A weight in pounds is converted to kilograms first, the same way every weight-based tool on this site does it, so the baseline is worked out on one basis.
Exercise adds to that baseline at roughly 355 ml (about 12 US fl oz) for every 30 minutes, scaled linearly — 15 minutes adds half of that, 90 minutes adds three times it. The total is then divided by 250 ml and rounded to the nearest whole glass, purely as a more familiar way to picture the same figure.
None of this is a personalised prescription: it does not know your climate, your health, or anything about you beyond weight and exercise time. See the FAQ below for what it leaves out.
Frequently asked questions
Where do these numbers come from?
There is no single universal medical formula for daily water needs — this uses two commonly cited rules of thumb: about 33 ml per kilogram of body weight, plus roughly 355 ml (about 12 fl oz) for every 30 minutes of exercise. They are reasonable starting points, not a figure derived for you personally. Individual needs vary with climate, health conditions, pregnancy and breastfeeding, and medication, among other things.
Does this account for climate or altitude?
No — it is a simple baseline from weight and exercise alone. Heat, humidity and high altitude all increase fluid loss, so treat this figure as a floor and drink more in those conditions, especially around exercise.
Is this medical advice?
No. This is a general estimate from two rules of thumb, not a hydration plan tailored to you. Anyone with a kidney, heart or other condition affecting fluid balance should follow their clinician's guidance instead of a generic calculator.