Water Intake Calculator
How much water a day, from weight and activity.
Water Intake Calculator estimates your daily fluid target from body weight, age, exercise, climate and pregnancy or breastfeeding status, then shows it in litres, millilitres, cups and fluid ounces and splits out the share that normally comes from food. The arithmetic runs in your browser and nothing is uploaded.
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Runs entirely on your device. No file or text you enter here is uploaded. How to verify it.
This is a calculation tool, not medical advice. The result is an estimate from a published formula and cannot account for your individual circumstances. Talk to a healthcare professional about anything that matters.
How to use Water Intake Calculator
- Enter your weight and age.
- Add your daily exercise, your climate and whether you are pregnant or breastfeeding.
- Read the total, and the part of it you need to drink rather than eat.
Questions about Water Intake Calculator
Where does the eight glasses a day rule come from?
It is usually traced to a 1945 US Food and Nutrition Board note suggesting about 2.5 litres a day. The very next sentence said most of that quantity is already present in prepared food, and that sentence is the one history dropped. No trial has ever tested eight glasses as a target for anybody.
Do tea and coffee count towards the total?
Yes. At ordinary intakes the diuretic effect of caffeine is smaller than the water in the cup, so tea and coffee are a net gain rather than a loss. Milk, juice and soft drinks count too, though the last two bring a good deal of sugar with them.
How much of my water really comes from food?
Around a fifth on a typical mixed diet, and closer to a third if you eat plenty of fruit, vegetables, soup and yoghurt. The tool lets you say which describes you, because that choice moves the amount you actually need to drink by several hundred millilitres a day.
Can you drink too much water?
Yes, although it takes some doing. Taking in litres of plain water faster than the kidneys can clear it dilutes blood sodium, which is what lies behind the collapses seen at endurance events and in drinking challenges. Thirst stops most people long before that point.
Should I treat this figure as a target?
No. It is arithmetic built on a rule of thumb, and it knows nothing about your sweat rate, your kidneys, your medication or the weather where you are. Anyone living with heart or kidney disease may have been given a fluid limit deliberately lower than anything here, and that limit is the one that counts.
Is Water Intake Calculator really free, with no limits?
Yes. There is no account, no daily cap, no file-size tier and no watermark, because there is no server cost to recover. The site is funded by clearly disclosed partner recommendations on the Partners page, never by metering the tools.
Are my files or text uploaded when I use Water Intake Calculator?
No. Everything is processed by JavaScript running in your browser, on your device. You can verify it: open your browser's developer tools, switch to the Network tab, and use the tool. You will see no request carrying your data — because there is nowhere for it to go.