Daily Water Intake Calculator
Enter your details for a rough, editable hydration planning estimate. No sign-up, no ads, and the math runs entirely in your browser.
There is no universal formula for a medically correct daily intake. This calculator applies a 33 ml per kilogram planning heuristic, then simple activity and climate adjustments. Treat the result as a starting estimate, not a prescription or a required amount of plain water.
Educational estimate only, not medical advice. It may not be appropriate during pregnancy, illness, endurance exercise, or for people with heart, kidney, liver, or other conditions affecting fluid balance. Follow clinician guidance and any fluid restriction.
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 rough planning estimate, shown in litres and glasses.
The formula
The starting figure is 33 ml per kilogram of body weight. For a 70 kg adult that is 2,310 ml. This is a product heuristic, not a National Academies or public-health prescription. Two deliberately simple adjustments are then added:
- 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. The fixed additions do not measure sweat loss and should not be used for clinical care or endurance-sport planning.
Context: National Academies reference values describe total water from food and beverages and emphasize variation between people and conditions.
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. The clamp limits extreme output, but it does not make the result medically appropriate for every body or health condition.
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.
Keep an editable reminder, not a rigid score
WaterWise logs a glass in one tap and keeps the goal adjustable. Free, offline, no ads.
▶ Get WaterWise freeFrequently asked questions
How much water should I drink a day?
There is no universal number. This calculator uses a rough weight-based planning formula, while National Academies reference values describe total water from food and every beverage. Individual needs vary.
Does exercise change how much water I need?
Exercise can increase fluid loss, but the amount varies with sweat rate, duration, intensity, clothing, and weather. The calculator's fixed activity additions are planning heuristics, not medical recommendations.
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.