Diet & fitness
Water Intake Calculator
Estimate how much water to drink each day from your body weight, exercise, and climate — free, no sign-up.
With the Institute of Medicine reference
Your details
About you
About a fifth of your water typically comes from food, so the figure to drink is a little lower. Thirst and pale-yellow urine are the best everyday guides.
Your target
Daily water
For reference, the Institute of Medicine suggests about 3.7 L of total water a day (beverages plus food) for men.
An estimate from body weight, activity, and climate — hydration needs vary with health, altitude, and conditions. Drink more when sweating heavily. General information, not medical advice.
How the estimate works
- 01
Start with body weight
A common heuristic is about 35 ml of water per kg of body weight per day — close to the familiar half-your-bodyweight-in-ounces rule.
- 02
Add for exercise
Sweat loses fluid, so we add roughly 355 ml (12 oz) for every 30 minutes of activity. Heavy or long sessions need more.
- 03
Adjust for climate
Hot or humid conditions raise your needs. The estimate nudges the target up, but listen to thirst on tough days.
What changes your needs
Food counts
About 20% of water intake comes from food, so the amount you actually drink is a bit below the total.
Heat and altitude
Both increase fluid loss. Add more in hot weather or at elevation.
Illness
Fever, vomiting, or diarrhea raise needs. Pregnancy and breastfeeding do too.
The simplest gauge
Pale-yellow urine and rarely feeling thirsty usually mean you're well hydrated.
Questions
- How much water should I drink a day?
- A reasonable estimate is about 35 ml per kg of body weight, plus more for exercise and heat. The Institute of Medicine's adequate intake is roughly 3.7 L total water a day for men and 2.7 L for women, including water from food.
- Does coffee or tea count?
- Yes. Despite their reputation, normal amounts of coffee and tea contribute to hydration. Most fluids count toward your total.
- Can I drink too much water?
- Rarely, but it's possible. Drinking very large amounts quickly can dilute blood sodium (hyponatremia). Spread intake through the day rather than forcing large volumes at once.
- Is the '8 glasses a day' rule correct?
- It's a rough guide, not a rule. Eight 8 oz glasses is about 1.9 L, which is in the right ballpark for many people but low for larger or very active individuals.