How to use it
- Choose who you're calculating for.
- Enter your daily minutes of exercise or physical work.
- Tick intense exercise or hot weather if they apply.
- Optionally measure your own sweat rate for a personal estimate.
How the estimate works
The base values are the adequate intakes set by the European Food Safety Authority (EFSA). They cover all water you take in: plain water, other drinks and the water in food. About 20% typically comes from food, so the calculator shows both your total and the part to drink.
| Group | Total water a day (EFSA) |
|---|---|
| Women (14+) | 2.0 L (68 fl oz) |
| Men (14+) | 2.5 L (85 fl oz) |
| Pregnant women | 2.3 L (78 fl oz) |
| Breastfeeding women | 2.7 L (91 fl oz) |
| Children 4–8 | 1.6 L (54 fl oz) |
The U.S. National Academies set higher adequate intakes: about 3.7 L (125 fl oz) for men and 2.7 L (91 fl oz) for women, including food. The difference reflects different methods, not a disagreement about health. Both assume moderate temperatures and activity.
Extra water for exercise
Sweat losses during exercise typically range from about 0.5 to 2 liters per hour. The calculator adds:
- 0.5–1 L (17–34 fl oz) per hour of normal exercise,
- 1–2 L (34–68 fl oz) per hour for intense exercise or hot conditions.
Example: a woman who exercises 60 minutes a day: 2.0 L base + 0.5–1 L = 2.5–3.0 L total, of which about 2.1–2.6 L (71–88 fl oz) from drinks, roughly 9–11 8-oz glasses.
Measure your own sweat rate
Sweat rates vary a lot between people. To measure yours, tap "Measure my sweat rate" and:
- weigh yourself before a workout (after using the bathroom, in minimal clothing),
- track how much you drink during it,
- weigh yourself again right after, after toweling off.
Sweat rate = (weight before − weight after + fluid drunk) ÷ hours. Each pound lost is about 16 fl oz. The calculator then uses your own rate for the exercise extra.
Signs you're drinking enough
For most healthy people, thirst is a good guide. Pale straw-colored urine is a sign of good hydration; dark yellow urine suggests you need more. Drink more in hot weather, at high altitude, during illness with fever, vomiting or diarrhea, and when breastfeeding.
During long, sweaty workouts you also lose sodium; a sports drink can help alongside water. Drinking huge amounts of plain water very quickly can be dangerous (hyponatremia), so spread your intake through the day.
Health conditions
If you have heart failure, kidney disease or another condition that affects fluid balance, your doctor may recommend a specific limit; follow that instead of this estimate. For babies under 6 months, breast milk or formula covers water needs.
This calculator is informational and isn't medical advice. Everything is calculated in your browser.
Frequently asked questions
How much water should I drink a day?
It varies. EFSA suggests about 2 L of total water for women and 2.5 L for men; the U.S. National Academies suggest about 2.7 L and 3.7 L. Around 20% usually comes from food.
Is 8 glasses of water a day right?
Eight 8-oz glasses (64 fl oz, about 1.9 L) is a reasonable rule of thumb for drinks, but needs vary with size, activity and climate.
Do coffee and tea count?
Yes. All drinks count toward your fluid intake, including coffee and tea in moderate amounts.
How much extra water do I need when exercising?
Typically 0.5–1 L (17–34 fl oz) per hour of exercise, and up to 2 L per hour in heat or intense sessions.
Can you drink too much water?
Yes. Drinking very large amounts quickly can dilute sodium in the blood. Spread intake through the day and use thirst as a guide.
Sources
- National Academies: Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
- EFSA Dietary Reference Values (DRV Finder)
Last reviewed: November 13, 2026 · Kitpebble editorial team
Change log
- : Content, sources and calculations reviewed.
- : Sources expanded; FAQ and content reviewed.
For general information only; not medical advice or a diagnosis. How we write and review our pages