Water Intake Calculator

The daily amount comes from the Adequate Intake levels for total water, which count water from drinks and from food. The optional sweat check uses the weigh-in method that the American College of Sports Medicine describes.

Formulas

How it works, step by step

1. First, the calculator picks the reference amount for your sex and shows it in liters or US fluid ounces.
2. Then it shows about 80% of that amount as the share that comes from drinks.
3. For the sweat check, it also treats one kilogram of body weight as one liter of fluid.
4. Finally, it compares your percent weight loss with the 2% line from the ACSM position stand.

Worked example

Someone who weighs 80 kg before a session and 79 kg after, and who drinks 0.5 L during it, has lost 1 kg net, which is 1.25% of body weight and shows as 1.3%. Their sweat loss comes to 1 + 0.5 = 1.5 L. The weight loss stays under the 2% line.

Accuracy and limits

The report describes the reference amounts as adequate intakes for healthy, sedentary people in a temperate climate. However, it says people who are very active or live in hot climates may need more, and it notes that very active people regularly exposed to heat often need six liters or more a day.

Sweat rates differ widely between people. For that reason, the ACSM position stand recommends a plan that fits your own sweat rate, and it says you can estimate that rate by weighing yourself before and after exercise.

The position stand sets the goal of drinking during exercise as preventing a water deficit above 2% of body weight. It also aims to avoid large changes in electrolyte balance, so more is not always better.

• The reference covers healthy adults, because pregnancy, breastfeeding, and heart or kidney conditions change fluid needs.
• A weigh-in gives a rough answer, because clothes, a bathroom stop or food during the session all shift the scale.
• If you have a medical condition or take medication that affects fluids, ask a clinician for personal advice.

Sources

1. National Academies. Report sets dietary intake levels for water, salt, and potassium to maintain health and reduce chronic disease risk (news release on the Dietary Reference Intakes for water; last updated February 11, 2004). Used for: The 3.7 L and 2.7 L total water reference intakes and who may need more.
2. American College of Sports Medicine, Sawka MN, Burke LM, et al. Position stand: exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377-390. Used for: The 2% body-weight line and estimating sweat rate by weighing before and after exercise.

Sources and math last reviewed: November 4, 2026.