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Body Fat Calculator
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Water Intake Calculator
Estimate how much water to drink a day from the National Academies’ adequate intake, adjusted for exercise.
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How to use this calculator
Enter your values. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.
Official intake values
| Group | Total water per day |
|---|---|
| Men 19+ | 3.7 L |
| Women 19+ | 2.7 L |
| Pregnant | 3 L |
| Breastfeeding | 3.8 L |
| Boys 14–18 | 3.3 L |
| Girls 14–18 | 2.3 L |
| Boys 9–13 | 2.4 L |
| Girls 9–13 | 2.1 L |
| Children 4–8 | 1.7 L |
| Children 1–3 | 1.3 L |
Source: National Academies, Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005). These are adequate intakes for total water, from food and all drinks.
How the estimate works
drinks ≈ 80% × adequate intake
+ exercise minutes ÷ 60 × your sweat-loss estimate
The National Academies estimate that about 80% of total water comes from drinks (including coffee, tea and milk) and 20% from food. Exercise adds the fluid you sweat out; your sweat rate is the biggest unknown, so the tool lets you set it.
Signs you’re drinking enough
- Pale yellow urine
- Rarely feeling thirsty
- Body weight stable before and after exercise
Drinking far more than you need in a short time can dilute blood sodium (hyponatremia), especially in long endurance events.
Frequently asked questions
How much water should I drink a day?
About 3 L of drinks for men and 2.2 L for women on average, which is 80% of the National Academies’ total water intakes, plus more for exercise and heat.
Does coffee count toward water intake?
Yes. Caffeinated drinks still add to total water intake for regular drinkers.
Is 8 glasses a day right?
Eight 8-oz glasses (about 1.9 L) is a reasonable minimum for many people, but it isn’t an official recommendation.
About this tool
- Written by
- [Author: to be assigned]
- Reviewed by
- Expert review pending
- Last updated
- 31 Oct 2026
See our methodology and editorial policy. Think something’s off? Report an error with this tool.
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