Estimate how much water to drink each day based on your weight, exercise and the weather where you live.
“Eight glasses a day” is easy to remember, but a 110 lb office worker and a 210 lb construction worker in a Phoenix summer don’t need the same amount. A better starting point is your body weight, with extra water added for exercise and hot weather. This calculator does that sum and turns it into ounces, glasses and liters.
How much water should I drink a day?
A common guide is about 33 ml of water per kg of body weight, so a 70 kg adult needs around 2.3 liters. Add roughly 350 ml for every 30 minutes of exercise and more in hot weather. Food and other drinks count toward this total.
How the estimate is worked out
+ 0.35 L per 30 minutes of exercise
+ 0.5 to 0.75 L in hot climates
Base amount by weight
| Weight | Liters | Glasses (250 ml) |
|---|---|---|
| 50 kg | 1.7 | 7 |
| 60 kg | 2.0 | 8 |
| 70 kg | 2.3 | 9 |
| 80 kg | 2.6 | 11 |
| 90 kg | 3.0 | 12 |
| 100 kg | 3.3 | 13 |
Signs you’re drinking enough
Pale yellow urine and rarely feeling thirsty are the simplest signs. Dark urine, headaches and tiredness can mean you need more. People with kidney or heart conditions, and pregnant or breastfeeding women, should follow their doctor’s advice instead of a general calculator.
How to use the Water Intake Calculator
Enter your weight
Type your weight in kg or lb.
Add your exercise
Type the minutes you usually exercise or do hard physical work each day.
Choose your climate
Pick hot or very hot if you live or work in high temperatures, which raises your needs.
Read your daily goal
Your goal appears in US fluid ounces, with the number of 8-oz glasses and liters underneath.
Frequently asked questions
Is 8 glasses of water a day enough?
Eight 250 ml glasses is 2 liters, which suits many lighter adults in mild weather. Heavier or active people, and anyone in a hot climate, usually need more.
Does tea or coffee count?
Yes. Tea, coffee, milk and water-rich foods all add to your intake, though plain water is the best choice.
Can I drink too much water?
Yes, drinking very large amounts quickly can lower blood sodium. Spread your intake through the day and drink to thirst.
How much more water should I drink in hot weather?
More than usual, because you lose extra fluid through sweat. Choosing Hot or humid in the calculator adds about 17 oz, and Very hot adds about 25 oz.
Is this medical advice?
No. It’s a general estimate. If you have a health condition, ask your doctor how much fluid is right for you.
Sources and further reading
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Last reviewed: October 2026