Water calculator
Water intake calculator
How much water should you drink a day? Enter your age and sex to see how much to drink, worked out from health authorities' reference values, then add exercise and hot weather. No sign-up, and nothing you type leaves this page.
Your daily water
Enter your age and sex to see your daily water.
Make it your daily goal
Hydrolotl is a free water tracker where every drink fills a pet axolotl's tank. Set this amount as your daily goal and log each drink with one tap.
Workout sweat check
Your own sweat rate beats any average. Weigh yourself just before and just after a workout, note what you drank, and the calculator works out how much you sweated. It is the method described by the American College of Sports Medicine (ACSM) and the National Athletic Trainers' Association (NATA).
Weigh yourself in the same clothes both times. If you peed during the workout, the result will be a little high, because that weight wasn't sweat.
Fill in both weights and the workout length.
Daily water by age: the reference values
EFSA's values are total water, drinks plus food. The US National Academies give total water and the part that usually comes from drinks.
| Group | EFSA, total | US National Academies, total | of which from drinks |
|---|---|---|---|
| 1 year | 1.1–1.2 L (37–41 fl oz) | 1.3 L (44 fl oz) | 0.9 L (30 fl oz) |
| 2–3 years | 1.3 L (44 fl oz) | 1.3 L (44 fl oz) | 0.9 L (30 fl oz) |
| 4–8 years | 1.6 L (54 fl oz) | 1.7 L (57 fl oz) | 1.2 L (41 fl oz) |
| Boys 9–13 | 2.1 L (71 fl oz) | 2.4 L (81 fl oz) | 1.8 L (61 fl oz) |
| Girls 9–13 | 1.9 L (64 fl oz) | 2.1 L (71 fl oz) | 1.6 L (54 fl oz) |
| Boys 14–18 | 2.5 L (85 fl oz) | 3.3 L (112 fl oz) | 2.6 L (88 fl oz) |
| Girls 14–18 | 2.0 L (68 fl oz) | 2.3 L (78 fl oz) | 1.8 L (61 fl oz) |
| Men 19 and over | 2.5 L (85 fl oz) | 3.7 L (125 fl oz) | 3.0 L (101 fl oz) |
| Women 19 and over | 2.0 L (68 fl oz) | 2.7 L (91 fl oz) | 2.2 L (74 fl oz) |
| Pregnancy | 2.3 L (78 fl oz) | 3.0 L (101 fl oz) | 2.3 L (78 fl oz) |
| Breastfeeding | 2.7 L (91 fl oz) | 3.8 L (128 fl oz) | 3.1 L (105 fl oz) |
EFSA treats teenagers from 14 as adults, and NASEM's values for ages 1 to 3 cover the first two rows. EFSA's values apply to moderate temperatures and moderate activity, and NASEM says people who are physically active or in hot environments need more.
How the calculator works
The starting point is the adequate intake for your age and sex from two health authorities: the European Food Safety Authority (EFSA, 2010) and the US National Academies (NASEM, report released in 2004). An adequate intake is based on what groups of healthy people actually take in and is assumed to be enough. It is not a strict requirement: NASEM notes that wide ranges of intake are compatible with normal hydration.
Both values are total water, which includes the water in food. NASEM found that about 80% comes from drinks and 20% from food, and gives its own figures for drinks. EFSA gives only total water, so the calculator applies NASEM's 80% to EFSA's totals as its own estimate. The two authorities don't agree exactly, which is why you get a range.
Pregnancy and breastfeeding have their own values: EFSA adds 300 ml (10 fl oz) a day in pregnancy and about 700 ml (24 fl oz) while breastfeeding, and NASEM gives 3.0 L (101 fl oz) and 3.8 L (128 fl oz) of total water.
Exercise: sweat losses vary too much for one formula. NATA reports adult sweat rates during exercise of 0.5 to 4.0 L (17 to 135 fl oz) an hour and says fluid plans should be based on your own data, not population averages. So the calculator adds exercise only when you give it your sweat rate, which the workout sweat check works out from your weight before and after.
Hot weather: for adults (18 and over), the calculator raises the result to at least 2–3 L (68–101 fl oz) a day, following the World Health Organization's heat advice.
Why it doesn't ask for your weight: EFSA and NASEM set adults' values by age and sex, not body weight. Weight matters in the workout sweat check, where it measures sweat.
Glasses are 250 ml; on the US setting, cups are 8 fl oz (237 ml).
Questions
How much water should I drink a day?
For adults, EFSA gives 2.0 L (68 fl oz) a day for women and 2.5 L (85 fl oz) for men, and the US National Academies 2.7 L (91 fl oz) and 3.7 L (125 fl oz). These are total water, including food. From drinks alone, the US National Academies give about 2.2 L (74 fl oz) for women and 3.0 L (101 fl oz) for men. Taking 80% of EFSA's totals (our own estimate, because EFSA gives only total water) gives about 1.6 L (54 fl oz) and 2.0 L (68 fl oz).
Do tea, coffee and milk count?
Yes. The NHS says water, lower-fat milk and lower-sugar drinks, including tea and coffee, all count toward your daily intake. The US National Academies found no convincing evidence that caffeine leads to a lasting water deficit.
Does food count?
Yes. About a fifth of the water people take in comes from food (NASEM). Cucumber, lettuce and watermelon, for example, are more than 90% water.
How much more should I drink when I exercise?
Up to what you lose in sweat, and that differs a lot between people: from 0.5 to 4.0 L (17 to 135 fl oz) an hour in adults, according to NATA. Weigh yourself before and after a workout to find your own sweat rate. If you don't know it, drinking when you're thirsty during exercise is most likely a safe way to avoid drinking too much, according to NATA.
Can you drink too much water?
Yes, but it is rare. Drinking large amounts very quickly can overwhelm the kidneys, which can clear only about 0.7–1.0 L (24–34 fl oz) an hour, and lead to dangerously low blood sodium (hyponatremia). Spread your drinks through the day.
Do older adults need a different amount?
No: EFSA and the US National Academies give older adults the same values as younger adults. But thirst becomes a less reliable signal with age, so regular drinking habits help.
Sources
- EFSA (2010). Scientific Opinion on Dietary Reference Values for water
- EFSA (2017). Dietary Reference Values for nutrients: summary report
- Institute of Medicine, National Academies (2005). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, chapter 4: Water
- National Academies (2004). Report sets dietary intake levels for water, salt and potassium
- McDermott et al. (2017). National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active
- American College of Sports Medicine, Sawka et al. (2007). Exercise and fluid replacement
- World Health Organization. Heat and health
- CDC (2026). About Heat and Your Health
- CDC (2024). Protect Yourself From the Dangers of Extreme Heat
- NHS. Water, drinks and your health
- NHS. Drinks and cups for babies and young children
- USDA Agricultural Research Service. FoodData Central
This calculator gives general information, not medical advice. If you have a health condition or your doctor has given you a fluid limit, follow their advice.
Keep reading
How Much Water Should You Drink a Day?
EFSA's adequate intake is about 2 liters a day for women and 2.5 for men, food included. What it means, what raises it, and how to set your own goal.
How Much Water Should You Drink When Exercising?
How much to drink before, during and after exercise: the 2% guideline, weighing yourself, thirst versus a plan, and why too much is risky.
How to Stay Hydrated in Hot Weather
How much to drink in hot weather, advice for working or exercising in the heat, who needs extra care, and how to tell heat exhaustion from heatstroke.