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How much water should I drink a day?
There is no single number. A common rule of thumb for healthy adults is half your body weight in pounds, as ounces of water a day. The table shows what it gives for a few body weights, for a mild climate and no exercise.
| Weight | Ounces | Liters | Cups |
|---|---|---|---|
| 100 lb | 50 | 1.5 | 6.5 |
| 120 lb | 60 | 1.8 | 7.5 |
| 128 lb | 64 | 1.9 | 8 |
| 135 lb | 68 | 2.0 | 8.5 |
| 150 lb | 75 | 2.2 | 9.5 |
| 170 lb | 85 | 2.5 | 10.5 |
| 200 lb | 100 | 3.0 | 12.5 |
| 250 lb | 125 | 3.7 | 15.5 |
How many ounces, liters and cups?
Ounces come first: half your weight in pounds. Liters follow by multiplying ounces by 0.0296, and cups by dividing ounces by 8. As one anchor, 64 ounces is 8 cups, or 1.9 liters. For the same numbers in other units, see water intake by weight, how many bottles of water a day and water bottles in a gallon.
Why the number is different for everyone
Body size, how active you are, the climate you live in, your health and the medicines you take all change how much water is right for you. A single figure cannot cover all of that, so use the estimate as a starting point and ask your doctor if you are unsure.
Men and women
A widely cited US reference puts total water at about 3.7 liters a day for men and 2.7 liters for women. That total counts all drinks and food, and about 20 percent of it usually comes from food, so plain water is only part of it. Ask your doctor what is right for you.
The 8 glasses idea
Eight 8-ounce glasses is 64 ounces, or 8 cups, about 1.9 liters. It is a popular rule of thumb with an unclear origin, not a research-based requirement.
Exercise and hot weather
Many people drink more when they exercise or when it is hot or humid. As common rules of thumb, add about 12 ounces for each 30 minutes of exercise and 16 ounces for hot or humid weather. The calculator on the home page adds both for you.
Spread it out
Instead of drinking a lot at once, many people spread the day's water across their waking hours. Spread over 16 waking hours, that is about 4.7 oz (139 mL) an hour. For why speed matters, read how much water is too much.
Frequently asked questions
How much water should I drink a day?
There is no single answer, because needs vary with body size, activity, climate and health. A common rule of thumb for healthy adults is half your weight in pounds, as ounces: 150 pounds is about 75 ounces, or 2.2 liters. Ask your doctor if you are unsure or have a health condition.
How many ounces of water should I drink a day?
A common rule of thumb is half your body weight in pounds, as ounces. That gives 64 ounces at 128 pounds, 75 ounces at 150 pounds and 100 ounces at 200 pounds. Add about 12 ounces for each 30 minutes of exercise. Needs differ, so ask your doctor if you are unsure.
How many liters of water should I drink a day?
Multiply your ounces by 0.0296 to get liters. By the half-your-weight rule of thumb, 150 pounds is 75 ounces, or about 2.2 liters, and 200 pounds is 100 ounces, or about 3.0 liters. Weight, exercise and heat change the amount, so the right number for you can differ.
How much water should men and women drink a day?
There is no fixed number for each sex. A widely cited US reference puts total water, from all drinks and food, at about 3.7 liters a day for men and 2.7 liters for women. Plain water is only part of that total. Ask your doctor what is right for you.
Is 2 liters of water a day enough?
Two liters is about 68 ounces, which matches the half-your-weight rule of thumb for a 135 pound adult. A 170 pound adult's rule of thumb is closer to 2.5 liters, or 85 ounces. Whether 2 liters is enough for you depends on size, activity, climate and health, so ask your doctor.
Do I need more water when I exercise or in hot weather?
Many people drink more when they exercise or when it is hot or humid. As a common rule of thumb, add about 12 ounces for each 30 minutes of exercise and 16 ounces for hot or humid weather. Needs vary, so ask your doctor if you have a health condition.