Last updated
Water intake by weight: the half-your-weight rule
A common rule of thumb is to drink about half your body weight, in pounds, as ounces of water a day. You may also see it written as drink half your body weight in water, or half your body weight in ounces of water. They all mean the same sum: a 160 pound adult gets 80 ounces, which is 10 cups or about 2.4 liters.
This is a common rule of thumb, not a prescription: half your weight in pounds, as ounces. It is a starting point for a healthy adult, and your own needs can differ. This rule is for people. Dogs and cats need different amounts, so for a pet see how much water a dog needs.
How to work out water intake by weight
- Find your weight in pounds. If you know it in kilograms, multiply by 2.2046.
- Halve the pounds. The result is a common rule of thumb for daily ounces of water.
- Divide the ounces by 8 to get cups, or by your bottle size to get bottles.
- Multiply the ounces by 0.0296 to get liters.
- Add 12 ounces for each 30 minutes of exercise and 16 ounces for hot or humid weather, or use the water intake calculator to do it for you.
Water intake by weight chart in pounds
Each row shows the rule of thumb for a mild climate and no exercise. Bottles are 16.9 ounces (500 mL).
| Weight (lb) | Ounces | Liters | Cups | Bottles (16.9 fl oz) |
|---|---|---|---|---|
| 100 | 50 | 1.5 | 6.5 | 3.0 |
| 110 | 55 | 1.6 | 7 | 3.3 |
| 120 | 60 | 1.8 | 7.5 | 3.6 |
| 130 | 65 | 1.9 | 8 | 3.8 |
| 140 | 70 | 2.1 | 9 | 4.1 |
| 150 | 75 | 2.2 | 9.5 | 4.4 |
| 160 | 80 | 2.4 | 10 | 4.7 |
| 170 | 85 | 2.5 | 10.5 | 5.0 |
| 180 | 90 | 2.7 | 11.5 | 5.3 |
| 190 | 95 | 2.8 | 12 | 5.6 |
| 200 | 100 | 3.0 | 12.5 | 5.9 |
| 210 | 105 | 3.1 | 13 | 6.2 |
| 220 | 110 | 3.3 | 14 | 6.5 |
| 230 | 115 | 3.4 | 14.5 | 6.8 |
| 240 | 120 | 3.5 | 15 | 7.1 |
| 250 | 125 | 3.7 | 15.5 | 7.4 |
Water intake by weight chart in kilograms
Use this chart for water intake per kg: each weight from 45 to 115 kg is converted to pounds first, then halved. Liters (spelled litres in many countries) are in the L column.
| Weight (kg) | Pounds | Ounces | Liters | Cups | Bottles (16.9 fl oz) |
|---|---|---|---|---|---|
| 45 | 99.2 | 50 | 1.5 | 6 | 2.9 |
| 50 | 110.2 | 55 | 1.6 | 7 | 3.3 |
| 55 | 121.3 | 61 | 1.8 | 7.5 | 3.6 |
| 60 | 132.3 | 66 | 2.0 | 8.5 | 3.9 |
| 65 | 143.3 | 72 | 2.1 | 9 | 4.2 |
| 70 | 154.3 | 77 | 2.3 | 9.5 | 4.6 |
| 75 | 165.3 | 83 | 2.4 | 10.5 | 4.9 |
| 80 | 176.4 | 88 | 2.6 | 11 | 5.2 |
| 85 | 187.4 | 94 | 2.8 | 11.5 | 5.5 |
| 90 | 198.4 | 99 | 2.9 | 12.5 | 5.9 |
| 95 | 209.4 | 105 | 3.1 | 13 | 6.2 |
| 100 | 220.5 | 110 | 3.3 | 14 | 6.5 |
| 105 | 231.5 | 116 | 3.4 | 14.5 | 6.8 |
| 110 | 242.5 | 121 | 3.6 | 15 | 7.2 |
| 115 | 253.5 | 127 | 3.7 | 16 | 7.5 |
Add exercise and hot weather
The weight rule leaves out exercise and heat. As common rules of thumb, add 12 ounces for each 30 minutes of exercise and 16 ounces for hot or humid weather. A 160 pound adult who exercises for 60 minutes gets 80 + 24 = 104 ounces, and 120 ounces on a hot or humid day. The calculator on the home page adds both for you.
Weight rule or 8 glasses?
Eight 8-ounce glasses is 64 ounces, or 8 cups. That is one number for everyone, while the weight rule scales with body size: 100 pounds gives 50 ounces and 200 pounds gives 100. The 8 glasses idea is a popular rule of thumb with an unclear origin, not a research-based requirement. Use either one as a starting point.
Frequently asked questions
How do you calculate water intake by weight?
Use a common rule of thumb: drink about half your body weight, in pounds, as ounces of water. A 160 pound adult gets 80 ounces, which is about 2.4 liters or 10 cups. If you know your weight in kilograms, multiply by 2.2046 first. Add more for exercise and heat.
Is drinking half your body weight in ounces right?
It is a popular rule of thumb, not a rule that fits everyone. It gives a simple starting number for a healthy adult, such as 100 ounces for 200 pounds. Your own needs can differ with activity, climate, health and medicines, so ask your doctor if you are unsure.
How much water should I drink a day by weight in kilograms?
Multiply your weight in kilograms by about 1.1 to get ounces, because kilograms times 2.2046 gives pounds and half of that is ounces. A 70 kilogram adult gets about 77 ounces, or 2.3 liters. Put another way, that is about 33 milliliters for each kilogram.
How much water should a 200 pound person drink?
By the half-your-weight rule of thumb, a 200 pound adult gets 100 ounces a day with no extra exercise or heat. That is about 3.0 liters, 12.5 cups or 5.9 bottles of 16.9 ounces. Add 12 ounces for each 30 minutes of exercise, and ask your doctor if you are unsure.
Does the weight rule change with age?
This rule uses weight only, not age, and it is meant for healthy adults 18 and older. Older adults, teenagers and children can have different needs, so this page gives no age-based numbers. Ask your doctor or a pediatrician about the amount that is right for the person you have in mind.
Why is my number different from the 8 glasses a day rule?
The 8 glasses rule means 64 ounces, about 1.9 liters, for everyone. The weight rule scales with body size: 150 pounds gives 75 ounces, while 100 pounds gives 50. Both are rules of thumb, so use the result as a starting point and adjust with your doctor's advice.