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How to estimate your daily water intake
- Enter your weight and choose pounds or kilograms.
- Enter the minutes you exercise on a typical day, from 0 to 300.
- Choose Mild or Hot or humid for your climate.
- Read your general estimate in ounces, liters, cups and bottles, and pick your bottle size.
- Spread the water across the day, and ask your doctor if you are pregnant or breastfeeding, have kidney or heart conditions, or take medication that affects fluids.
How the estimate works
This is a common rule of thumb, not a prescription: half your weight in pounds as ounces, plus 12 ounces for every 30 minutes of exercise, plus 16 ounces in hot or humid weather.
The weight part comes first. If you enter kilograms, the calculator multiplies by 2.2046 to get pounds, then halves the pounds. Exercise is pro-rated by the minute, so 45 minutes adds 18 ounces. The total is then shown as liters (1 ounce is 29.5735 milliliters), cups (8 ounces each) and bottles of the size you pick.
| What you enter | What the estimate adds |
|---|---|
| Weight | 0.5 oz for every pound |
| Exercise | 12 oz for every 30 minutes |
| Hot or humid climate | 16 oz |
Daily water intake by weight
Here is what the same rule of thumb gives for four body weights in a mild climate with no exercise. For every weight from 100 to 250 pounds, and for kilograms, see water intake by weight.
| Weight | Ounces | Liters |
|---|---|---|
| 100 lb | 50 oz | 1.5 L |
| 150 lb | 75 oz | 2.2 L |
| 200 lb | 100 oz | 3.0 L |
| 250 lb | 125 oz | 3.7 L |
Cups, bottles and gallons
A cup here is 8 fluid ounces, so 75 ounces is 9.5 cups. To turn an estimate into bottles of your own size, see how many bottles of water a day.
A US gallon is 128 ounces, or 16 cups. See water bottles in a gallon for bottles and liters in a gallon.
Who this estimate is for
This estimate is for healthy adults 18 and older. It is general information, not medical advice, and it does not know your health, your medicines or whether you are pregnant or breastfeeding. Talk to your doctor if any of those apply, and read the medical disclaimer for more.
For a broader guide to daily amounts, see how much water to drink a day. For the other side of the question, see how much water is too much.
Frequently asked questions
How do you calculate how much water to drink a day?
Start with a common rule of thumb: half your body weight in pounds, as ounces. A 150 pound adult gets 75 ounces. Then add 12 ounces for every 30 minutes of exercise and 16 ounces in hot or humid weather. This calculator does the sum for you and shows the result in ounces, liters, cups and bottles.
Can I enter my weight in kilograms and see liters?
Yes. Choose kg in the weight box, and the calculator converts kilograms to pounds (1 kg is about 2.2046 lb) before halving. A 68 kilogram adult with 30 minutes of exercise gets about 87 ounces, which is about 2.6 liters. Results always show ounces, liters, cups and bottles side by side.
Does age change the result?
No. This calculator does not use age, and it is built for healthy adults 18 and older. It has no calculation for children or teenagers. Needs also change with health, medicines and pregnancy, so ask your doctor if you are unsure about the right amount for you or for a child.
What if I am pregnant or breastfeeding?
The pregnancy or breastfeeding box does not change your number. Needs are usually higher at these times, so a general estimate may be too low. Talk to your doctor or midwife about how much water is right for you, and use the number here only as a starting point for that conversation.
How much extra water should I add for exercise or hot weather?
The calculator adds 12 ounces for every 30 minutes of exercise and 16 ounces for hot or humid weather. Both are common rules of thumb, not exact needs. A 200 pound adult who exercises 60 minutes in hot weather gets 140 ounces, about 4.1 liters, instead of 100 ounces.
How many cups and bottles is my estimate?
Divide your ounces by 8 for cups, and by your bottle size for bottles. An estimate of 75 ounces is about 9.5 cups, shown to the nearest half cup, and about 4.4 bottles of 16.9 ounces. Pick a different bottle size, from 8 ounces to 1 liter, and the bottle count updates.