Daily Water Intake Calculator

The tool needs two things: your weight in kilograms and an activity level. It allows 33 ml for every kilogram, then adds a flat half litre if you choose Moderate or anything above it:

litres = weight × 33 ÷ 1000, + 0.5 if activity is Moderate, Active or Very active

The defaults, 70 kg at Moderate, give 2.31 + 0.5 = 2.8 L a day. This is a simple body-weight rule of thumb, not an official target. It is an estimate, not a diagnosis, and it doesn't replace a fluid amount a doctor has given you for a medical reason.

The activity menu has five options, but the tool treats them as just two groups. Sedentary and Light add nothing; Moderate, Active and Very active all add the same 0.5 L:

So moving from Moderate to Very active changes nothing, while moving from Light to Moderate jumps the answer by half a litre. If your activity sits on that line, run both and look at the difference.

The US National Academies (Institute of Medicine, 2004) set an Adequate Intake for total water of 3.7 L a day for men and 2.7 L for women aged 19 to 30. That total includes water from food as well as drinks, and drinks supply about 81% of it, which is roughly 3.0 L for men and 2.2 L for women from fluids. The figures are based on what healthy people typically consume. They are not a target for preventing disease, and people who are active in hot weather need more.

This tool takes no account of sex, food, climate or heat. Treat its number as one reference point, and those official figures as another.

Under the litres, the tool shows a cup count labelled 250 ml. It is the litre figure divided by 0.25 L and rounded to a whole cup, so the default 2.81 L shows as 11 cups (11.2 before rounding).

Glasses and bottles vary a lot in size, so if yours aren't 250 ml, divide the litre figure by your own glass size instead. A 330 ml glass, for example, means about 8.5 glasses for 2.81 L.