Water Intake Calculator

How It Works

How much water you need depends mostly on your size: bigger bodies need more. This calculator starts from the common weight-based guideline of about 30–35 ml of water per kilogram of body weight a day, using 33 ml per kg as the midpoint, then adds 500 ml per hour of exercise and 500 ml more in hot conditions. The result covers all fluids — water, tea, coffee and other drinks — not just water from a glass.

For comparison, the U.S. National Academies set an Adequate Intake for total water — drinks plus the water in food — of 3.7 litres a day for men and 2.7 litres for women, of which about 3.0 and 2.2 litres come from drinks. Roughly a fifth of daily water comes from food, which is why the drinking target is lower than the total-water figure.

Worked Example

A 70 kg adult who exercises for an hour: the base estimate is 70 × 33 ml = 2,310 ml (2.3 litres), plus 500 ml for the exercise hour, giving 2,810 ml — about 2.8 litres, 95 fl oz or 11.7 cups a day. Without exercise the same person would need about 2,100–2,450 ml (the 30–35 ml per kg range).

How to Use This Calculator

Enter your weight, your daily exercise hours and your climate. The result shows your estimated daily intake in millilitres, litres, fluid ounces and cups, plus the guideline range for your weight.

Tips and Practical Advice

Spread intake through the day and drink more when you sweat heavily. Thirst, pale-yellow urine and steady energy are better day-to-day guides than any fixed number. People with heart, kidney or liver conditions, or on a prescribed fluid limit, should follow their clinician’s advice instead.

Sources: weight-based guideline of 30–35 ml/kg/day; U.S. National Academies, Dietary Reference Intakes for Water (2005). Reviewed Nov 13, 2026.

Frequently Asked Questions