Water Intake Calculator
Instant results as you type.
A water intake calculator estimates how much water to drink daily, based on your body weight plus extra for exercise. It uses a widely cited rule of thumb — around 35 ml per kilogram of body weight, plus roughly 350 ml for every 30 minutes of activity. Enter your weight in kilograms or in pounds; US readers get the target back in fluid ounces and 8 fl oz cups rather than litres. Real needs vary with climate, health, and diet, so treat this as a sensible starting target rather than a medical instruction. It runs on your device.
How to use it
- Pick your units, then enter your weight — kilograms, or pounds if you chose the US or UK setting.
- Add how many minutes you exercise on a typical day.
- See your daily target in litres and 250 ml glasses, or in fluid ounces and 8 fl oz cups on the US setting.
Examples
- 70 kg with no exercise → 2.45 litres, about 10 glasses.
- 154 lb with no exercise → 82.67 fl oz, about 10 cups — the same amount of water.
- 70 kg with an hour of exercise → 3.15 litres.
Frequently asked questions
- How much water should I drink a day?
- A common guideline is about 35 ml per kilogram of body weight, so roughly 2.5 litres for a 70 kg adult, plus more when you exercise or the weather is hot. Thirst and pale-yellow urine are practical everyday indicators that you are drinking enough.
- Does tea or coffee count toward intake?
- Yes, largely. Despite the common belief, moderate tea and coffee contribute to daily fluid intake — the mild diuretic effect of caffeine does not cancel out the water they contain. Plain water is still the better default for most of your intake.
- Should I drink more in hot weather?
- Yes. Heat and humidity increase fluid loss through sweat, sometimes considerably. Add extra beyond this estimate on hot days, during illness with fever, and at high altitude.
- Can you drink too much water?
- It is possible but uncommon. Drinking extreme amounts in a short time can dilute blood sodium dangerously, a condition called hyponatraemia. Spreading intake through the day rather than forcing large volumes at once avoids the risk entirely.