Water Intake Calculator
How much water should you drink a day? Get a simple estimate from your weight and activity, in litres, glasses and fluid ounces.
Key facts
- European guidelines set an adequate total water intake of about 2.0 litres a day for women and 2.5 litres for men, from drinks and food together.
- About a fifth of that usually comes from food, so tea, milk, soup, fruit and vegetables all count.
- Thirst and pale-yellow urine are good everyday signs that you are drinking enough.
How the calculator works
Water (litres) = 0.033 × weight (kg) + extra for activity
The activity extra is 0 litres if you are sedentary, about 0.35 L if lightly active, 0.5 L if moderately active, 0.75 L if very active and 1 L for athletes. The result is rounded to 0.1 L.
For a 70 kg moderately active adult that is 0.033 × 70 + 0.5 = 2.8 litres, or about 11 glasses of 250 ml.
When to drink more
- Hot weather and high altitude: often 0.5 to 1 litre more a day.
- Exercise: sweat losses can be 0.5 to 2 litres an hour. Drink before and after, and during long sessions.
- Illness with fever, vomiting or diarrhoea.
- Pregnancy and breastfeeding: needs go up (talk to your midwife or doctor).
Drinking enough while fasting
During Ramadan or other fasts, spread your water between iftar and suhoor rather than drinking it all at once: a glass or two at iftar, a little every hour in the evening, and one or two at suhoor. Watery foods (soups, fruit, yoghurt and cucumber) help too, and very salty or fried foods make you thirstier the next day.
Can you drink too much?
Yes, though it is rare. Drinking very large amounts in a short time, for example several litres during a long race without salt, can dilute the sodium in your blood (hyponatraemia). Drink to thirst during long events, and don’t force down water you don’t want.
Kidney or heart disease? Some conditions need a fluid limit. Follow your doctor’s advice rather than this calculator.
Count glasses with one tap
Calculators give an estimate. Log your weight and food for two weeks and the TDEE Calculator app works out what your body really burns, then keeps your target up to date.
- Measured TDEE from your own weight trend and food log
- Food diary with 356 everyday foods from around the world and a barcode scanner
- AI coach and photo calories: snap your plate, check the estimate, add it
- 74 languages, metric or US units, Ramadan mode and reminders
- Private: your log stays on your phone. No ads, no trackers
Water intake calculator questions
Is 8 glasses a day right for everyone?
It is a fair rule of thumb, but needs vary with your size, activity and climate. Larger and more active people need more; smaller people in cool weather may need less.
Do tea and coffee count?
Yes. Tea and coffee in normal amounts count towards your daily fluid. Milk, soup and juice count too, though water is the best everyday drink.
How do I know if I’m drinking enough?
You rarely feel thirsty and your urine is pale yellow. Dark urine, headaches and tiredness can be signs you need more.
Does drinking water help with weight loss?
Water has no calories, so replacing sugary drinks with water cuts calories. Drinking a glass before meals may also help some people eat a little less.
How much water should I drink when exercising?
Drink a glass or two in the hours before, sip during sessions longer than an hour, and drink afterwards until your urine is pale again.
Sources
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459. doi.org/10.2903/j.efsa.2010.1459
- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academies Press; 2005. nap.nationalacademies.org/10925