Daily Water Intake Calculator

Use this calculator to easily calculate your recommended daily water intake you need to keep yourself healthy and at peak physical and mental performance. If you are asking yourself how much water should you drink per day our water calculator will calculate that for you in cups, ounces (oz), and milliliters.

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Estimating optimal daily water intake

Our water calculator will help you easily estimate how much water you need per day including how much of it you will need to drink in the form of fluids (pure water or beverages). The outputs of our water intake calculator are in liters, milliliters, cups and ounces. Of course, these are estimates based on population averages so consulting your physician or nutritionist is always recommended before making changes to your water consumption or exercise routine.

Estimating your recommended total daily water intake and thus optimal hydration requires the estimation of your total daily energy expenditure (TDEE) which measures how much energy (in kCal, kilocalories) you expend during a typical day. We use a rule that expresses water needs in relation to energy requirements in ml/kCal. Energy requirements are strongly evidence-based in each age and gender group based on extensive research which takes into account body size and activity level which are crucial determinants of energy expenditure which must be met by dietary energy intake. Such measures of expenditure use highly accurate methods and thus TDEE has been set based on solid data rather than the compromise inherent in the Adequate Intake estimations made for water. Those same determinants are also applicable to water utilization and balance and this provides an argument for pegging water/fluid intake recommendations to the better studied energy recommendations. The extent to which water intake and requirements are determined by energy intake and expenditure is understudied but in the clinical setting it has long been practice to supply 1 ml per kCal administered by tube to patients unable to take in food or fluids [1].

Water input in the human body comes from three main sources: water and other beverages, food, and as a side-effect of metabolic processes. Since water and beverages are only a part of the input, our calculator will output both your total water intake recommendation as well as how much of it you need to get through drinking fluids. You should be careful to not confuse how much water you need with how much water you need to drink. The latter is usually only around 4/5 of the total, thus you actually need to drink slightly less water than your total daily needs. Say you need a total of 70 ounces per day, this would mean that you need to drink just 56 oz of water (7 cups), the rest will enter your body through food and metabolic processes. See our water content for selected foods table below.

water intake

Water is ejected from the body in the form of urine, gastrointestinal processes, as part of respiration, and through sweating and other insensible outputs. Your body is always trying to maintain homeostasis and since sweating varies considerably depending on physical activity and how hot the environment is, it can result in drastically different water drinking needs. Some adjustments in the amount of water may be needed if you are subject to such influences as explained below.

General water drinking recommendations

Below we present the general recommended amount of water intake based on recommendations from the . These are population-wide adequate intake estimations and are thus less preferred than the personalized calculations from our calculator above.

EFSA stands for European Food Safety Authority and IOM stands for the U.S. Institute of Medicine, data is based on reference 3.. Water intake is in L/day (liters per day / litres per day).

Adequate Water intake recommendations
Age group ESFA IOM
Total water intakeFluid intakeTotal water intakeFliud intake
0-6 mo. 0.68 (milk) 0.68 (milk) 0.70 0.70
6-12 mo. 0.80 - 1.00 0.64 - 0.80 0.80 0.80
1-2 years 1.10 - 1.20 0.88 - 0.90 N/A N/A
2-3 years 1.30 1.00 N/A N/A
1-3 years N/A N/A 1.30 0.90
4-8 years 1.60 1.20 1.70 1.20
9-13 y. Boys 2.10 1.60 2.40 1.80
9-13 y. Girls 1.90 1.50 2.10 1.60
Boys 14+ & Adult Men 2.50 2.00 3.30 2.60
Girls 14+ & Adult Women 2.00 1.60 2.30 1.80
Pregnant Women 2.30 1.84 2.60 1.90
Lactating Women 2.60 2.10 3.40 2.80
Elderly As adults As adults As adults As adults

It should be noted that, in general, our bodies are fairly good at estimating how much water one needs on a daily basis and this happens via the mechanism of thirst. If you are thirsty, you should certainly drink water no matter what any kind of estimation is telling you.

Adjustments for climate, excessive sweating & pregnancy

If you are a woman and you are pregnant, you will require more water per day and you will require even more water if you are lactating. Our water drinking calculator will perform the adjustments for you based on a compromise between tables provided by the European Food Safety Authority (EFSA) and the U.S. Institute of Medicine (IOM) [3].

The results of this water calculator assume most of your day is spent in a moderate climate. If you live in a hot climate and spend your days mostly outside or in a non-climatized building, then you will need to adjust your water intake upwards, but we are not aware of good research estimating by how much depending on temperature, exposure to sun, etc.

The results of this tool also assume you are not subject to vigorous physical activity in a hot environment, in which cases losses in excess of 3L per hour are possible [4] and you need to adjust your fluid intake accordingly to compensate for that. Cold climates have less of an effect, but extremely cold climates may result in increased energy needs to compensate for the heat loss and thus you may need a higher water intake.

Benefits of staying optimally hydrated

One of the reasons to use a hydration calculator is to maintain a healthy life, but adequate water intake is also linked to benefits for the treatment of some conditions as well as mental state improvement. Water comprises from 75% body weight in infants to 55% in elderly and is essential for cellular homeostasis and life so it is no wonder it is so essential to one's health. Amazingly, a recent large sample-size study found that in a free-living population from German, Spain, and Greece only approximately 60% of participants were properly hydrated while about 20% were hyperhydrated and 20% dehydrated on average over a seven-day period [5].

Kidney health

The kidneys function more efficiently in the presence of an abundant water supply. If the kidneys economize on water, producing a more concentrated urine, these is a greater cost in energy and more wear on their tissues. This is especially likely to occur when the kidneys are under stress, for example when the diet contains excessive amounts of salt or toxic substances that need to be eliminated. Consequently, drinking enough water helps protect this vital organ [1].

There is strong evidence that recurrence of kidney stones is much less likely when your hydration status is good due to the increased urine volume [1].

Sports performance

During challenging athletic events, it is not uncommon for athletes to lose 6–10% of body weight in sweat loss, thus leading to dehydration if fluids have not been adequately replenished. Decrements in physical performance in athletes have been observed under much lower levels of dehydration: as little as 2% Under relatively mild levels of dehydration, individuals engaging in rigorous physical activity will experience decrements in performance related to reduced endurance, increased fatigue, altered thermoregulatory capability, reduced motivation, and increased perceived effort. Rehydration can reverse these deficits, and also reduce oxidative stress induced by exercise and dehydration. Hypohydration appears to have a more significant impact on high-intensity and endurance activity such as tennis and long-distance running than on anaerobic activities such as weight lifting or on shorter-duration activities, such as rowing [1].

Children are especially prone to voluntary dehydration so child athletes and children doing sports in hot climate should start well-hydrated to avoid any potential issues.

Cognitive abilities

A body of studies examined by Popkin et. al [1] indicates that low to moderate dehydration may negatively affect cognitive performance. Rather than indicating that the effects of hydration or water ingestion on cognition are contradictory, many of the studies differ significantly in methodology and in measurement of cognitive behaviors. In studies in which dehydration were induced, most combined heat and exercise, thus it is difficult to disentangle the effects of dehydration on cognitive performance in temperate conditions, from the effects of heat and exercise. In practice, relatively little is known about the mechanism of mild dehydration’s effects on mental performance. It has been proposed that mild dehydration acts as a physiological stressor which competes with and draws attention from cognitive processes. However, research on this hypothesis is limited and merits further exploration.

A more recent study by came to the conclusion that even though traditionally a 2% or more body water deficit was thought to produce cognitive performance decrements more recent literature suggests that even mild dehydration – a body water loss of 1–2% – can impair cognitive performance. Counseling clients about their health and wellbeing should include conveying the importance of water for normal body functioning, as well as its effects on physical and cognitive performance. [7]

Headache prevention and treatment

A 2012 randomized control trial by Spigt et. al [9] suggests that considering the observed positive subjective effects, it seems reasonable to recommend headache patients to try this non-invasive intervention for a short period of time to see whether they experience improvement. The study is critiqued for low statistical power and biases due to partial unblinding of participants by Price A. and Burls A. (2015) [10], so the jury appears to still be out on this one.

Type II Diabetes

Epidemiological research has demonstrated that low daily total water intake is associated with increased diagnosis of hyperglycemia and a study confirms that 3 days of low total water intake in people with type 2 diabetes mellitus acutely impairs blood glucose response during an oral glucose tolerance test via cortisol but not RAAS-mediated glucose regulation, where RAAS stands for renin-angiotensin-aldosterone system [8].

Constipation and water intake

Constipation, characterized by slow gastrointestinal transit, small, hard stools, and difficulty in passing stool, has a number of causes including medication use, inadequate fiber intake, poor diet, and illness. Inadequate fluid consumption is touted as a common culprit in constipation and increasing fluid intake is a frequently recommended treatment. However, the evidence suggests that increasing fluids is only of usefulness in individuals in a hypohydrated state and is of little utility in properly hydrated people. In young children with chronic constipation, increasing daily water intake by 50% did not affect constipation scores. [1]

Heart rate and blood pressure

Water intake acutely reduces heart rate and increases blood pressure in people with normal or increased blood pressure. The effects of water intake on the pressor effect and heart rate occur within 15–20 minutes of drinking water and can last for up to 60 minutes. Water ingestion is also beneficial in preventing vasovagal reaction with syncope in blood donors at high risk for post-donation syncope [1].

Bronchopulmonary disorders

There is strong evidence from meta analyses of randomized controlled trials that exercise related asthma is linked with low fluid intake. Thus, increasing water intake has a beneficial effect on the condition [1].

Skin and skin conditions

There is no evidence to support the notion that drinking more water will improve the skin complexion, remove wrinkles, acne, or help with other skin conditions. Increasing the water intake will improve the skin thickness and density in persons with low initial water intake, but if you are already drinking adequate amounts of water, increasing that will not be beneficial for your skin [1].

All-risk mortality

A prospective study in 2017 found that "there was no survival advantage in association with higher total or plain water intake in men or women in this national cohort" [6] so even though proper water intake appears to have certain benefits they may not go as far as increasing your live span. However, it is unclear what size of effect the study was powered to exclude. While all-risk mortality is an important measurement, quality of life and achievements should be taken into account when considering the usefulness of knowing how much water you need to drink and of abiding to those recommendations.

Weight loss by drinking more water?

A 2014 non-controlled study [11] of 50 female overweight women established that drinking water three times a day 30 min before breakfast, lunch, and dinner, to a total of 1.5L above the recommended daily amount, resulted in a decrease in body weight, BMI, sum of skinfold thickness, and appetite scores of the participants over an 8-week period and establishes the role of drinking excessive water in weight reduction, body fat reduction, and appetite suppression of participants. Thus, water drinking induced increase in sympathetic activity is an important and unrecognized component of daily energy expenditure. Thus, water has the potential to be a cost free intervention useful as adjunctive treatment in overweight and obese individuals and using a water drinking calculator such as ours to estimate the recommended amount would be an essential part of such an effort.

A systematic review of the impact of water intake on energy intake and weight status by Daniels & Popkin [12] finds reasonable agreement among a number of single meal studies that replacing water with sugar-sweetened beverages will increase energy intake by about 8%, possibly leading to weight gains. There is sparse data on replacing sugar-sweetened beverages with water and/or milk and juices, but the available studies point to modest improvements in reducing energy intake as well as reducing risk of being overweight. Most of the studies are observation and there is a distinct lack of randomized controlled trials and long-term studies of the effects of replacing other beverages with water. Still, it appears that the available literature suggests some positive effects on weight-loss from drinking more water before eating and for replacing sugar-sweetened drinks with water.

Water content in foods

Below is a reference table for the water content in selected foods, based on Altman P. "Blood and Other Body Fluids" (1961), Federation of American Societies for Experimental Biology as cited in Popkin B. M., D’Anci K. E., Rosenberg I. H. (2010) "Water, Hydration and Health" [1].

Water content in selected foods
Water percentageFood item
100% Water
90-99% Fat-free milk, cantaloupe, strawberries, watermelon, lettuce, cabbage, celery, spinach, pickles, squash (cooked)
80-89% Fruit juice, yogurt, apples, grapes, oranges, carrots, broccoli (cooked), pears, pineapple
70-79% Bananas, avocados, cottage cheese, ricotta cheese, potato (baked), corn (cooked), shrimp
60-69% Pasta, legumes, salmon, ice cream, chicken breast
50-59% Ground beef, hot dogs, feta cheese, tenderloin steak (cooked)
40-49% Pizza
30-39% Cheddar cheese, bagels, bread
20-29% Pepperoni sausage, cake, biscuits
10-19% Butter, margarine, raisins
1-9% Walnuts, peanuts (dry roasted), chocolate chip cookies, crackers, cereals, pretzels, taco shells, peanut butter
0% Oils, sugars


[1] Popkin B. M., D’Anci K. E., Rosenberg I. H. (2010) "Water, Hydration and Health" Nutrition Reviews 68(8):439–458

[2] Riebl S. K., Davy B. M. (2013) "The Hydration Equation: Update on Water Balance and Cognitive Performance" ACSM’s Health & Fitness Journal 17(6):21–28

[3] Gandy J. (2015) "Water intake: validity of population assessment and recommendations" European Journal of Nutrition, 54(Suppl 2):11–16

[4] Rehrer N.J., Burke L.M. (1996) "Sweat losses during various sports" Australian Journal of Nutrition and Dietetics 53(Suppl 4):13–16

[5] Malisova O., Athanasatou A., Pepa A., Husemann M., Domnik K., Braun H., Mora-Rodriguez R., Ortega J.F., Fernandez-Elias V.E., Kapsokefalou M. (2016) "Water Intake and Hydration Indices in Healthy European Adults: The European Hydration Research Study (EHRS)" Nutrients 8(4):204

[6] Kant A. K., Graubard B. I. (2017) "A prospective study of water intake and subsequent risk of all-cause mortality in a national cohort" The American Journal of Clinical Nutrition 105(1):212–220

[7] Riebl S. K., Davy B. M. (2013) "The Hydration Equation: Update on Water Balance and Cognitive Performance." ACSM’s Health & Fitness Journal 17(6):21–28

[8] Johnson E.C., Bardis C.N., Jansen L.T., Adams J.D., Kirkland T.W., Kavouras S.A. (2017) "Reduced water intake deteriorates glucose regulation in patients with type 2 diabetes" Nutritional Research 43:25-32

[9] Spigt M., Weerkamp N., Troost J., van Schayck C.P., Knottnerus J.A. (2012) "A randomized trial on the effects of regular water intake in patients with recurrent headaches" Family Practice 29(4):370-5

[10] Price A., Burls A. (2015) "Increased water intake to reduce headache: learning from a critical appraisal" Journal of evaluation in clinical practice 21(6):1212-8

[11] Vij V.A.K., Joshi A.S. (2014) "Effect of excessive water intake on body weight, body mass index, body fat, and appetite of overweight female participants" Journal of Natural Science, Biology, and Medicine 5(2):340–344.

[12] Daniels M. C., Popkin B. M. (2010) "The impact of water intake on energy intake and weight status: a systematic review" Nutrition Reviews 68(9):505–521

Cite this calculator & page

If you'd like to cite this online calculator resource and information as provided on the page, you can use the following citation:
Georgiev G.Z., "Water Intake Calculator", [online] Available at: https://www.gigacalculator.com/calculators/water-intake-calculator.php URL [Accessed Date: 18 Feb, 2019].