Water intake calculator
How much water should I drink a day?
For most adults, about 1.5 to 3.5 litres of drinks a day, depending on your weight, sex, activity and climate. Enter yours to get your own number, with every part explained.
Your daily goal
2 500ml
2.5 litres of drinks a day, about 10 glasses of 250 ml.
How it's calculated
- Body weight70 kg · 33 ml per kg2 310 ml
- SexNot set+200 ml
- ActivitySlightly active+0 ml
- ClimateTemperate+0 ml
Rounded to the nearest 50 ml and kept between 1 500 and 5 000 ml. The goal is for drinks; food adds water on top. Based on EFSA, the National Academies and Yamada 2022.
Track it every day with Hydra
The same formula in the app, plus extra water on workout days, and every drink counted by what your body keeps.
Not medical advice. These are general estimates for healthy adults. If you have a heart or kidney condition, or your doctor has told you how much to drink, follow their advice.
The formula
How your water goal is calculated
The goal starts from your body weight, 33 ml per kilogram (about half an ounce per pound), which fits a typical, lightly active adult. Then it adds or takes away water for the things that change how much you need.
The total is rounded to the nearest 50 ml and kept between 1.5 and 5 litres. A 70 kg adult, sex not set, slightly active, in a temperate climate gets 2 310 + 200 = 2 510, so 2 500 ml.
The result falls between the European (EFSA) and US (National Academies) recommendations for drinks. Men need a little more at the same weight, and very active people about a litre more than people who sit most of the day (Yamada 2022, in Science).
It's the same formula Hydra uses for your daily goal in the app, where you can tap the goal to see this breakdown at any time. For a ready-made table, see water intake by body weight.
| Part | Choice | ml |
|---|---|---|
| Weight | per kg | 33 |
| Sex | Female | +0 |
| Not set | +200 | |
| Male | +400 | |
| Activity | Sitting | −250 |
| Slightly active | +0 | |
| Active | +500 | |
| Very active | +1 000 | |
| Climate | Cool | −200 |
| Temperate | +0 | |
| Hot | +500 | |
| Hot day replaces climate | 25–29 °C | +250 |
| 30–34 °C | +500 | |
| 35 °C and up | +750 | |
| Female only | Pregnant | +300 |
| Breastfeeding | +700 |
Questions
Water intake, answered
How much water should I drink a day?
For most healthy adults, about 1.5 to 3.5 litres of drinks a day (roughly 50 to 120 oz). A good starting point is 33 ml per kilogram of body weight, plus more for men, for an active lifestyle and for hot weather. A 70 kg adult who is lightly active in a temperate climate needs about 2.5 litres. Food adds water on top. Use the calculator above for your own number.
Is 8 glasses of water a day right?
Eight 250 ml glasses is 2 litres, which is close for many adults but too little for larger or active people, and more than a small, sedentary person needs. Your weight, sex, activity and climate matter more than a fixed number of glasses. More in is 8 glasses a day a myth?
Does coffee count towards my water intake?
Yes. Studies found no dehydration with moderate daily coffee intake, so coffee and tea count like water. Milk counts a little more than water, because the body keeps more of it; alcohol makes you lose water. Hydra counts every drink by its own hydration factor. More in does coffee dehydrate you?
How much more water should I drink when it's hot or when I exercise?
If you live in a hot climate, about 500 ml more a day. On a single hot day, about 250 ml more from 25 °C, 500 ml from 30 °C and 750 ml from 35 °C. Regular training adds about 500 ml a day, daily hard training or physical work about 1 litre. Long, sweaty sessions can need more: exercise can cost 0.5 to 2 litres of sweat an hour. See how much water to drink when you exercise and how much water to drink in hot weather.
How much water should I drink when pregnant or breastfeeding?
EFSA recommends about 300 ml more a day during pregnancy and about 700 ml more while breastfeeding, on top of the usual goal. Choose Female in the calculator to add it, or read water intake in pregnancy and breastfeeding.
Can you drink too much water?
Yes. Drinking very large amounts in a short time can dilute the sodium in your blood, which is dangerous. Spread your drinks over the day and don't force yourself far past thirst. People with heart or kidney conditions may need to limit fluids: follow your doctor's advice.
Is this calculator medical advice?
No. It gives general estimates for healthy adults. If you have a medical condition, follow your doctor's guidance on fluids.
Sources
The studies behind the numbers
The same sources Hydra lists in the app (History › Sources).
- Daily goalVariation in human water turnover associated with environmental and lifestyle factors
- Daily goalScientific opinion on dietary reference values for water
- Daily goalDietary reference intakes for water, potassium, sodium, chloride, and sulfate
- ActivityAmerican College of Sports Medicine position stand: exercise and fluid replacement
- Drink factorsA randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index
- Coffee factorNo evidence of dehydration with moderate daily coffee intake
- Alcohol factorsThe diuretic action of alcohol in man
- Alcohol factorsThe diuretic action of weak and strong alcoholic beverages in elderly men
Now drink to it.
Hydra turns this number into your daily goal, adapts it to workouts and hot days, and counts every drink by what your body keeps.