water intake calculator
A quick daily estimate from your body weight, exercise and climate, in litres, ounces and glasses, with the official reference figures alongside.
fashion law journal · tools deskupdated 25 sep 2026general guidance
Quick answer: most healthy adults need roughly 30 to 35 ml of fluid per kg of body weight a day (about ½ oz per lb), more with exercise or heat. The US National Academies’ reference total water intake, from food and drink, is about 3.7 litres for men and 2.7 litres for women, and around 80% of that comes from drinks.
If you have a kidney, heart or liver condition, or have been told to limit fluids, follow your doctor’s advice instead.
official daily water guidance
| source | women | men | notes |
|---|---|---|---|
| US National Academies | 2.7 L total | 3.7 L total | adequate intake, from food and drink |
| European Food Safety Authority | 2.0 L total | 2.5 L total | +0.3 L pregnant, +0.7 L breastfeeding |
| UK NHS Eatwell Guide | 6 to 8 glasses of fluid a day | water, milk, sugar-free drinks, tea and coffee count | |
signs you’re getting enough
- Pale straw-coloured urine is the simplest everyday check.
- Thirst is a reliable guide for most healthy adults. You don’t need to force down water you don’t want.
- Tea, coffee, milk and water-rich foods (fruit, soup, vegetables) all count towards your intake.
- Drinking far too much too quickly can be dangerous (hyponatraemia), especially during long endurance events.
water intake questions
How much water should I drink a day?
A common starting point is 30 to 35 ml per kg of body weight (about half an ounce per pound). For a 65 kg person that’s about 2 to 2.3 litres of drinks a day, plus more for exercise and hot weather.
Is 8 glasses a day a real rule?
It’s a rough rule of thumb, not a scientific requirement. It’s close to many adults’ needs from drinks alone, but body size, activity and climate change the number.
Does coffee count towards water intake?
Yes. At normal amounts, the fluid in coffee and tea outweighs their mild diuretic effect, so they count towards your daily total.
How much more should I drink when exercising?
Roughly 350 to 500 ml extra for each 30 minutes of exercise, more in heat or if you sweat heavily.
General information only, not medical advice. Individual needs vary. Sources: US National Academies Dietary Reference Intakes (2005), EFSA Scientific Opinion on water (2010), NHS Eatwell Guide. More tools: body shape calculator.