Free water intake calculator
How much water should you drink today?
Enter your weight, activity and climate to get a daily water goal, a drinking schedule and a tracker.
A water intake calculator estimates how much to drink each day from your body size, activity and climate. US guidelines put total water at about 3.7 liters for men and 2.7 liters for women, and about 80% of that comes from drinks.[2]
Daily water at a glance
- US guideline: about 3.7 L (125 oz) of total water a day for men and 2.7 L (91 oz) for women, from all drinks and food.[2]
- From drinks: about 3.0 L (13 cups) for men and 2.2 L (9 cups) for women. Food supplies roughly the other 20%.[1]
- Europe: EFSA sets 2.5 L of total water for men and 2.0 L for women.[5]
- Measured needs: a 2022 study of 5,604 people in 23 countries found that the 8-glasses rule is probably too high for most people in most situations.[3][4]
- Coffee counts: US guidelines include caffeinated drinks in daily water.[2]
- Upper pace: healthy kidneys can clear roughly 0.7 to 1.0 L of water an hour.[13]
How to use the water intake calculator
- Enter your sex, age and weight. Women can add pregnancy or breastfeeding.
- Pick your usual activity. Tick the athlete box only if you train competitively.
- Enter today’s climate. Typical outdoor temperature, humidity and altitude all change how much water the body uses.
- Add today’s workout, if any. Enter the minutes, or your own sweat rate from the sweat test in the results.
- Use the results. You get a goal from drinks, a comparison with the guidelines, a drinking schedule, a tracker for today, a sweat test and a urine-color check.
How much water should you drink a day?
Most adults need about 2 to 3 liters (68 to 101 oz) a day from drinks, with food adding the rest. US guidelines set about 3.0 L from drinks for men and 2.2 L for women. Body size, activity and heat move the number up or down.[1]
These guideline amounts are adequate intakes. They reflect what healthy, well-hydrated people in the US typically consume, not a strict minimum. The National Academies added that most healthy people meet their needs by letting thirst guide them, and that people who are very active or live in hot climates may need more.[2]
| Group | US: total water a day | US: from drinks | Europe (EFSA): total water a day |
|---|---|---|---|
| Men, 19 and older | 3.7 L (125 oz) | 3.0 L (101 oz), about 13 cups | 2.5 L (85 oz) |
| Women, 19 and older | 2.7 L (91 oz) | 2.2 L (74 oz), about 9 cups | 2.0 L (68 oz) |
| Pregnancy | 3.0 L (101 oz) | 2.3 L (78 oz), about 10 cups | 2.3 L (78 oz) |
| Breastfeeding | 3.8 L (128 oz) | 3.1 L (105 oz), about 13 cups | 2.7 L (91 oz) |
| Boys, 14 to 18 | 3.3 L (112 oz) | 2.6 L (88 oz), about 11 cups | 2.5 L (85 oz) (adult value) |
| Girls, 14 to 18 | 2.3 L (78 oz) | 1.8 L (61 oz), about 8 cups | 2.0 L (68 oz) (adult value) |
How this water calculator works
The calculator uses the 2022 Science equation for daily water turnover, the total water the body takes in and loses. Researchers built it from deuterium measurements in 5,604 people aged 8 days to 96 years in 23 countries.[3]
water turnover (mL/day) = 1076 × PAL + 14.34 × weight (kg) + 374.9 × sex + 5.823 × humidity (%) + 1070 × athlete + 104.6 × HDI + 0.4726 × altitude (m) − 0.3529 × age² + 24.78 × age + 1.865 × temperature² − 19.66 × temperature (°C) − 713.1
PAL is the physical activity level. The calculator uses the middle of each FAO/WHO/UNU band: 1.55 for mostly sitting, 1.85 for active and 2.2 for very active.[6] Sex is 1 for men and 0 for women. HDI is 0 for countries with high human development, 1 for medium and 2 for low.[3]
Turnover is not the same as drinking water. About 15% of turnover is water the body makes from food or absorbs from the air, so food and drinks supply about 85%.[3][4] Food then supplies about 20% of that intake.[2] The calculator’s goal from drinks is therefore turnover × 0.85 × 0.8. This last step is our calculation from the two sources.
Example: a 30-year-old woman weighing 150 lb, mostly sitting, at 68°F and 50% humidity has a predicted turnover of about 3.0 L. Her goal from drinks is about 2.0 L, or 69 oz.
| Change | Water the body uses a day | Goal from drinks a day |
|---|---|---|
| 10 kg (22 lb) more body weight | +143 mL | +3 oz |
| Male instead of female, same weight | +375 mL | +9 oz |
| Active instead of mostly sitting | +323 mL | +7 oz |
| Very active instead of mostly sitting | +699 mL | +16 oz |
| Competitive athlete | +1,070 mL | +25 oz |
| 86°F (30°C) instead of 68°F (20°C) | +736 mL | +17 oz |
| 20 points more humidity | +116 mL | +3 oz |
| 1,000 m (3,281 ft) higher altitude | +473 mL | +11 oz |
| Age 60 instead of 30 | −209 mL | −5 oz |
| Medium instead of high human development country | +105 mL | +2 oz |
Is drinking 8 glasses of water a day right?
Not for most people. The team behind the 2022 study said the 8-glasses advice, about 2 liters, is probably too high for most people in most situations. They found no single amount fits everyone.[4]
Two things explain the gap. First, the rule ignores the water in food and in other drinks, including coffee and tea.[2] Second, needs vary widely. In the study, water turnover was highest in men aged 20 to 35, at about 4.2 liters a day, and fell to about 2.5 liters in people in their 90s.[4]
How much water should you drink based on your weight?
Weight matters less than most calculators suggest. In the Science equation, each extra 10 kg (22 lb) adds about 143 mL of daily water use. Activity, heat and sex move the number more.[3]
| Body weight | Women, goal from drinks | Men, goal from drinks | "Half your weight in ounces" rule |
|---|---|---|---|
| 120 lb (54 kg) | 65 oz | 73 oz | 60 oz |
| 150 lb (68 kg) | 69 oz | 78 oz | 75 oz |
| 180 lb (82 kg) | 74 oz | 82 oz | 90 oz |
| 210 lb (95 kg) | 78 oz | 87 oz | 105 oz |
| 240 lb (109 kg) | 83 oz | 91 oz | 120 oz |
The table assumes a 35-year-old who is mostly sitting, at 68°F and 50% humidity. Enter your own details in the calculator for a personal number.
How much water should you drink when you exercise?
Drink enough to keep weight loss during exercise under 2% of body weight, the American College of Sports Medicine advises. Sweat rates vary a lot between people, so the ACSM recommends measuring your own by weighing before and after exercise.[7]
- Before: drink about 5 to 7 mL per kg of body weight at least four hours before exercise.[7]
- During: aim to replace sweat losses, but do not drink more than you sweat.[7]
- After: drink about 1.5 liters for every kilogram of body weight lost, ideally with salty food or a sports drink.[7]
- Long or hot sessions: drinks with electrolytes and carbohydrate can work better than water alone.[7]
The sweat test inside the calculator does this math for you. For recovery meals, see the guide to a diet for muscle recovery, and check your aerobic fitness with the VO2 max calculator.
How much water should you drink when pregnant or breastfeeding?
US guidelines set 3.0 liters of total water a day in pregnancy and 3.8 liters while breastfeeding, including about 2.3 and 3.1 liters from drinks. That is 0.3 and 1.1 liters more than for other women.[1]
EFSA adds 300 mL in pregnancy and 700 mL while breastfeeding to the usual 2.0 liters for women.[5] The calculator adds the US amounts when you choose pregnant or breastfeeding. Your doctor or midwife may advise differently, for example with swelling or high blood pressure.
Do coffee, tea and other drinks count?
Yes. Coffee, tea, milk, juice and other drinks all count toward daily water, according to US guidelines, which include caffeinated drinks in the total.[2]
A 2014 trial tested the old idea that coffee dehydrates. Fifty men who drank coffee regularly had four cups a day for three days, then the same amount of water. Total body water and blood and urine markers did not differ. The study was funded by a coffee-industry science group.[8] Large caffeine doses can still affect sleep. The caffeine calculator shows how much will be left at bedtime.
Food counts too. Fruits, vegetables, soups and coconut water are rich in water. See the guides to coconut water and super fruits for ideas.
How can you tell if you are drinking enough water?
Check thirst and urine color. Pale straw-colored urine usually means you are well hydrated. Dark yellow or amber means you need more. The 8-color urine chart by Armstrong and colleagues is the most widely used scale.[9]
Urine color is a rough guide, not a lab test. In one study, both an 8-color and a 7-color chart matched lab measures of urine concentration about 77% of the time.[11] The charts work best with urine in a clear cup rather than in the toilet bowl. Creatine, B vitamins and some medicines can change the color.[10] The urine-color check in the calculator uses the 8-color scale.
Can you drink too much water?
Yes, though it is rare in daily life. Healthy kidneys can clear roughly 0.7 to 1.0 liters an hour. Drinking much faster than that can dilute blood sodium, a condition called hyponatremia.[13]
The risk is highest in long endurance events. In a study of 488 runners at the 2002 Boston Marathon, 13% finished with hyponatremia and 0.6% with a critically low level. The strongest risk factor was gaining weight during the race, a sign of drinking more than they sweated.[12]
Early signs include headache, nausea, bloating and confusion, which can look like dehydration. Seek care if they appear after heavy drinking. People with heart, kidney or liver disease may need to limit fluids and should follow their doctor’s advice.
Simple ways to drink enough water
- Drink with every meal. Meals are an easy anchor, and food adds water too.
- Keep a bottle in sight. Use the tracker in the calculator to count it.
- Sip through the day. Spreading drinks out is easier on the body than drinking a lot at once.
- Drink more in heat and with exercise. These are the biggest drivers of extra need.
- Eat water-rich foods. Fruits and vegetables help hydration and skin. See the guide to a diet for healthy skin.
In Ayurveda, sipping warm water through the day is a traditional habit, especially for the Vata dosha. The free dosha quiz shows which dosha leads for you. If you fast, the intermittent fasting calculator plans your eating window, and water is fine during the fast.
What this water calculator cannot know
The equation predicts average water use for people like you. It explains about half of the differences between people, so your own needs can be higher or lower.[3] It cannot see your sweat rate unless you measure it, your diet’s water content, or health conditions and medicines that change fluid balance.
Use the number as a starting point, then adjust with thirst and urine color. Talk to a doctor if you are always thirsty, pass very large amounts of urine, or have been told to limit fluids.
More free tools for daily health decisions.
Water intake calculator FAQ
How much water should I drink a day?
US guidelines put total water at about 3.7 liters a day for men and 2.7 liters for women, from all drinks and food. About 80% of that comes from drinks: roughly 13 cups for men and 9 cups for women. Body size, activity and climate shift your own number, which the calculator above estimates.
How much water should I drink based on my weight?
Weight is one factor, not the whole answer. In the 2022 Science equation, each extra 10 kg (22 lb) of body weight adds about 143 mL (5 oz) of water turnover a day. Activity, sex, age, climate and altitude matter too, so enter all of them above.
Is drinking 8 glasses of water a day right?
Not for everyone. A 2022 study of 5,604 people found that the common 8-glasses advice is probably too high for most people in most situations, while very active people in hot climates may need more. Food and other drinks also count.
Does coffee or tea count toward water intake?
Yes. US guidelines count caffeinated drinks toward total water. In a 2014 trial, 50 regular coffee drinkers who had four cups a day showed no signs of dehydration compared with drinking the same amount of water. The study was funded by a coffee-industry science group.
How much water should I drink when I exercise?
It depends on your sweat rate, which ranges widely. The American College of Sports Medicine advises drinking enough to keep body-weight loss under 2% during exercise, and about 1.5 liters for every kilogram lost afterward. Use the sweat test in the calculator to find your rate.
How much water should I drink while pregnant or breastfeeding?
US guidelines set total water at 3.0 liters a day in pregnancy and 3.8 liters while breastfeeding, including about 2.3 and 3.1 liters from drinks. EFSA adds 300 mL in pregnancy and 700 mL while breastfeeding to the usual amount for women.
How can I tell if I am drinking enough water?
Thirst and urine color are the simplest checks. Pale straw-colored urine usually means you are well hydrated, and dark yellow means you need more. Urine color charts are most accurate with urine in a clear cup. Some vitamins and medicines change the color.
Can you drink too much water?
Yes. Healthy kidneys can clear roughly 0.7 to 1.0 liters an hour. Drinking much faster than that, especially during long endurance events, can dilute blood sodium and cause hyponatremia, which can be dangerous. Drink to thirst and sip through the day.
Do I need more water in hot weather?
Yes. In the 2022 Science study, water turnover rose with heat and humidity. For example, the equation adds about 1 liter a day going from 50 to 86 degrees F (10 to 30 degrees C), all else equal. Enter your typical outdoor temperature above.
How much water do I get from food?
About 20% of total water usually comes from food, according to US guidelines. Fruits, vegetables, soups and yogurt are rich in water. That is why the calculator shows a goal for drinks that is lower than your total water need.
Does drinking more water help with weight loss?
This calculator does not estimate weight change. Water has no calories, so swapping sugary drinks for water cuts calories, but the amount of water alone is not a proven weight-loss method. Talk to a doctor or dietitian for a weight plan.
Does this water calculator store my data?
No. The calculator runs in your browser. Your settings and today’s drink log are saved only in this browser. A copied link carries your settings inside the link, not your log.
Sources
- Institute of Medicine (2006). Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. Water. National Academies Press. nap.edu/read/11537/chapter/15
- National Academies (2004). Report sets dietary intake levels for water, salt, and potassium to maintain health and reduce chronic disease risk. nationalacademies.org/news/report-sets-dietary-intake-levels-for-water-salt-and-potassium-to-maintain-health-and-reduce-chronic-disease-risk
- Yamada Y, Zhang X, Henderson MET, et al. (2022). Variation in human water turnover associated with environmental and lifestyle factors. Science, 378(6622), 909-915. doi.org/10.1126/science.abm8668
- University of Aberdeen (2022). How much water do we really need? Comments from Professor John Speakman on the Science study. abdn.ac.uk/about/international/news/16566
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2010). Scientific Opinion on Dietary Reference Values for water. EFSA Journal, 8(3), 1459. doi.org/10.2903/j.efsa.2010.1459
- FAO, WHO and UNU (2004). Human energy requirements: report of a Joint FAO/WHO/UNU Expert Consultation. Physical activity level categories. fao.org/4/Y4249E/y4249e0j.htm
- American College of Sports Medicine; Sawka MN, Burke LM, Eichner ER, et al. (2007). Exercise and fluid replacement. Medicine and Science in Sports and Exercise, 39(2), 377-390. pubmed.ncbi.nlm.nih.gov/17277604
- Killer SC, Blannin AK, Jeukendrup AE (2014). No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS ONE, 9(1), e84154. pmc.ncbi.nlm.nih.gov/articles/PMC3886980
- Armstrong LE, Maresh CM, Castellani JW, et al. (1994). Urinary indices of hydration status. International Journal of Sport Nutrition, 4(3), 265-279. pubmed.ncbi.nlm.nih.gov/7987361
- Human Performance Resources by CHAMP (HPRC). How to accurately assess hydration status using urine color charts. hprc-online.org/nutrition/performance-nutrition/how-accurately-assess-hydration-status-using-urine-color-charts
- Arizona State University (2021). New urine color chart makes self-assessing hydration easier (Wardenaar and colleagues). news.asu.edu/20210507-discoveries-studies-provide-insight-advancements-self-assessing-hydration
- Almond CSD, Shin AY, Fortescue EB, et al. (2005). Hyponatremia among runners in the Boston Marathon. New England Journal of Medicine, 352(15), 1550-1556. pubmed.ncbi.nlm.nih.gov/15829535
- Institute of Medicine (2005). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academies Press. nap.edu/catalog/10925
This calculator gives an estimate for healthy adults, based on published equations and guidelines. It is not medical advice and cannot diagnose, treat or prevent any condition. If you have heart, kidney or liver disease, take medicines that affect fluid balance, or have been told to limit fluids, follow your doctor’s advice instead of this calculator.
