Daily Water Intake Calculator
Enter your details for a personalised daily hydration target. No sign-up, no ads, the math runs entirely in your browser.
A common evidence-based estimate for daily water intake is about 30–35 ml per kilogram of body weight: roughly 2.1–2.5 litres for a 70 kg adult, with more needed during exercise or in hot, humid weather. This calculator turns your weight, activity level, and climate into a personalised daily target, and every calculation runs on your device.
Educational estimate only, not medical advice. People with heart or kidney conditions should follow their doctor's guidance.
How this works
There is no hidden model here and no server call. The calculator is about ten lines of arithmetic that run in your browser, and the numbers below are the numbers it uses. They are checked by an automated test on every change to this site, so what is published here and what the tool actually does cannot drift apart.
Using the calculator
- Enter your weight in kilograms.
- Choose your activity level: sedentary, moderate, or active.
- Choose your climate: temperate, or hot and humid.
- Read the daily target, shown in litres and in glasses.
The formula
The starting figure is 33 ml per kilogram of body weight. For a 70 kg adult that is 2,310 ml. Two adjustments are then added on top of it:
- Moderate activity adds 350 ml.
- Active adds 700 ml instead, the two are alternatives, not cumulative.
- A hot or humid climate adds a further 500 ml, on top of whichever activity figure applies.
So the same 70 kg adult gets 2,310 ml when sedentary in a temperate climate, 2,660 ml when moderately active, and 3,510 ml when active in a hot climate. Anything the tool does not recognise as an activity level or a climate adds nothing at all, which means an unanswered question can only ever leave the estimate lower, never inflate it.
Where the maths stops
Weight is clamped to a range of 30 kg to 200 kg before any calculation runs. Type 10 and it is treated as 30; type 500 and it is treated as 200. A mistyped weight therefore cannot produce a target that nobody should be drinking towards.
The result is rounded to the nearest millilitre before it is displayed. Nothing you enter is stored, sent, or logged, the page keeps no record of it once you close the tab.
Knowing the target is the easy part
Hitting it every day is the hard part. WaterWise logs a glass in one tap and nudges you gently through the day. Free, offline, no ads.
â–¶ Get WaterWise freeFrequently asked questions
How much water should I drink a day?
A common starting point is about 33 ml of water per kilogram of body weight, adjusted up for exercise and hot weather. This calculator estimates that target for you; individual needs vary.
Does exercise change how much water I need?
Yes. Moderate activity adds roughly 350 ml and vigorous activity roughly 700 ml to your daily target to replace fluids lost through sweat.
Is this calculator medical advice?
No. It is an educational estimate. If you have a heart, kidney, or other condition that affects fluid intake, follow your doctor's guidance.