Water intake calculator by weight and exercise
The National Academies published total water figures of about 2.7 liters a day for women and 3.7 liters for men in 2004. Those figures count water from food and every drink, with about 20 percent coming from food. See the National Academies news release, checked October 1, 2026.
Rule of thumb
- Cups
- 11.5
- Liters
- 2.72
Half an ounce per pound from Medical News Today, plus 12 ounces per 30 minutes of exercise from UT Health San Antonio. This is a rule of thumb, not a requirement.
National Academies figure
Total water from drinks and food, from the 2004 report.
- Women
- 2.7 liters
91 ounces
11.4 cups - Men
- 3.7 liters
125 ounces
15.6 cups
These published figures stay the same when weight or exercise changes.
Change weight or exercise minutes to calculate the rule of thumb. Switching units converts the weight already entered.
A worked example with 160 lb and 30 minutes
Half an ounce per pound gives 160 × 0.5 = 80 ounces. The exercise addition is 12 × (30 ÷ 30) = 12 ounces.
The total is 80 + 12 = 92 ounces. In cups, 92 ÷ 8 = 11.5 cups. In liters, 92 × 0.0295735 = 2.72 liters.
The metric check is 72.57 kg ÷ 0.45359237 = 160.0 lb when rounded. That produces the same displayed result of 92.0 ounces, 11.5 cups and 2.72 liters.
For the National Academies figures, the approximate drink share is 80 percent of 91 ounces = 72.8 ounces for women and 80 percent of 125 ounces = 100 ounces for men. That share includes drinking water and other drinks.
Water figures in ounces, cups and liters
| Pounds | Ounces | Cups | Liters |
|---|---|---|---|
| 100 | 50.0 | 6.3 | 1.48 |
| 125 | 62.5 | 7.8 | 1.85 |
| 150 | 75.0 | 9.4 | 2.22 |
| 175 | 87.5 | 10.9 | 2.59 |
| 200 | 100.0 | 12.5 | 2.96 |
| 225 | 112.5 | 14.1 | 3.33 |
| 250 | 125.0 | 15.6 | 3.70 |
| Group | Total liters | Total ounces | Total cups | Drink share in ounces |
|---|---|---|---|---|
| Women | 2.7 | 91 | 11.4 | 72.8 |
| Men | 3.7 | 125 | 15.6 | 100 |
What the National Academies report said
The panel called these adequate intake levels. Women who appear adequately hydrated take in about 2.7 liters, or 91 ounces, of total water a day. Men average about 3.7 liters, or 125 ounces. The reference covers the expected needs of healthy, sedentary people in temperate climates.
The report says very physically active people and people in hot climates may need more. About 80 percent of total water comes from drinking water and other drinks, including caffeinated drinks. Food supplies the other 20 percent.
The panel did not offer a rule of thumb for how many glasses of water to drink. Juice, milk, coffee, tea, soda, fruits, vegetables and other foods all contribute water.
Where the rule of thumb comes from
Medical News Today gives weight in pounds × 0.5 = ounces of water per day. Its example uses 200 lb to get 100 ounces and notes that the amount can vary with physical activity.
UT Health San Antonio supplies the exercise add-on used here, 12 ounces for each 30 minutes of working out. For 45 minutes, that adds 18 ounces. Its article starts with two thirds of body weight, so this calculator uses only its exercise addition alongside the separate half ounce per pound rule.
The combined formula is a rule of thumb, not a requirement. It and the National Academies figure measure different things. The National Academies figure includes water in food and all drinks, while this calculation combines a weight formula with an exercise addition.
If you have a medical condition, follow your clinician's advice on fluids.
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Frequently asked questions
How much water does the National Academies figure include?
The 2004 figures are about 2.7 liters a day for women and 3.7 liters for men. Both include total water from food and all drinks.
Does water from food count?
Food contributes about 20 percent of total water in the National Academies report. Drinking water and other drinks contribute about 80 percent, including caffeinated drinks.
Where does the half ounce per pound rule come from?
Medical News Today describes multiplying weight in pounds by 0.5 to get ounces of water per day. It is a rule of thumb that can vary with physical activity.
How does the calculator add exercise?
It adds 12 ounces for every 30 minutes of exercise, using the add-on published by UT Health San Antonio. For 45 minutes, the addition is 18 ounces.
Sources and conversions
- National Academies news release on water intake, February 11, 2004, checked October 1, 2026.
- Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate, National Academies Press, checked October 1, 2026.
- How much water should I drink each day?, Medical News Today, updated December 9, 2024, checked October 1, 2026.
- UT Health San Antonio on water and exercise, Jason Adams, PA-C, July 2018, checked October 1, 2026.
The conversions used here are 1 US fluid ounce = 29.5735 milliliters and 1 cup = 8 US fluid ounces. For weight, 1 kilogram = 2.20462 pounds when rounded. The calculator divides kilograms by 0.45359237 to get pounds.
Compare a weight and exercise rule of thumb with the National Academies figures for total water from drinks and food.