Water Intake Calculator
Estimate daily water intake from body weight and minutes of activity: 33 mL per kg plus 0.5 L per active hour, in liters and fluid ounces. A rule of thumb. How it works
Use the Water Intake Calculator
About the Water Intake Calculator
This water intake calculator uses a rule of thumb: 33 mL per kilogram of body weight, plus 0.5 L for each hour of activity. At 70 kg with 30 minutes of activity that is 2.56 L a day, about 87 fl oz. The total counts all drinks and the water in food, and most healthy adults can go by thirst.
Daily water by body weight in kilograms
| Body weight | No activity | 30 minutes of activity | 60 minutes of activity |
|---|---|---|---|
| 50 kg | 1.65 L (56 fl oz) | 1.9 L (64 fl oz) | 2.15 L (73 fl oz) |
| 60 kg | 1.98 L (67 fl oz) | 2.23 L (75 fl oz) | 2.48 L (84 fl oz) |
| 70 kg | 2.31 L (78 fl oz) | 2.56 L (87 fl oz) | 2.81 L (95 fl oz) |
| 80 kg | 2.64 L (89 fl oz) | 2.89 L (98 fl oz) | 3.14 L (106 fl oz) |
| 90 kg | 2.97 L (100 fl oz) | 3.22 L (109 fl oz) | 3.47 L (117 fl oz) |
| 100 kg | 3.3 L (112 fl oz) | 3.55 L (120 fl oz) | 3.8 L (128 fl oz) |
| 110 kg | 3.63 L (123 fl oz) | 3.88 L (131 fl oz) | 4.13 L (140 fl oz) |
33 mL per kg plus 0.5 L per hour of activity, as the calculator shows it in Metric. Each extra 10 kg adds 0.33 L, and each 30 minutes of activity adds 0.25 L.
Daily water by body weight in pounds
| Body weight | No activity | 30 minutes of activity | 60 minutes of activity |
|---|---|---|---|
| 100 lb | 51 fl oz (1.5 L) | 59 fl oz (1.75 L) | 68 fl oz (2 L) |
| 125 lb | 63 fl oz (1.87 L) | 72 fl oz (2.12 L) | 80 fl oz (2.37 L) |
| 150 lb | 76 fl oz (2.25 L) | 84 fl oz (2.5 L) | 93 fl oz (2.75 L) |
| 175 lb | 89 fl oz (2.62 L) | 97 fl oz (2.87 L) | 105 fl oz (3.12 L) |
| 200 lb | 101 fl oz (2.99 L) | 110 fl oz (3.24 L) | 118 fl oz (3.49 L) |
| 225 lb | 114 fl oz (3.37 L) | 122 fl oz (3.62 L) | 131 fl oz (3.87 L) |
| 250 lb | 127 fl oz (3.74 L) | 135 fl oz (3.99 L) | 143 fl oz (4.24 L) |
The same rule as the calculator shows it in Imperial: pounds are divided by 2.2046 to get kilograms, and fluid ounces are US.
Methodology
Liters per day = weight in kg × 0.033 + (activity minutes ÷ 60) × 0.5, plus 0.3 L if you choose Pregnant or 1.1 L if you choose Breastfeeding. Pounds are divided by 2.2046226218. Liters are shown to two decimals and US fluid ounces (liters × 33.814) to a whole number. Weight can be 20 to 300 kg and activity 0 to 600 minutes a day.
Frequently asked questions
- How much water should I drink a day for my weight?
- By this rule, 33 mL per kg: 1.98 L at 60 kg, 2.64 L at 80 kg and 3.3 L at 100 kg before any activity. Add 0.25 L for every 30 minutes of activity. It is a rule of thumb and not an official requirement.
- How many ounces of water should I drink a day?
- In US fluid ounces the same rule gives 76 fl oz at 150 lb and 101 fl oz at 200 lb with no activity, and 84 and 110 fl oz with 30 minutes of activity. Switch to Imperial to enter pounds and read the result in fl oz.
- Do I need 8 glasses of water a day?
- There is no official glass count. The National Academies panel that set US water intake figures in 2004 declined to give a rule in glasses and reported that most healthy people meet their needs by letting thirst guide them. Eight 8 oz glasses come to 64 fl oz, or 1.9 L, which is what this rule gives a 50 kg person with 30 minutes of activity.
- Do coffee and tea count toward water intake?
- Yes. The National Academies count total water from all beverages, including caffeinated ones, and from food: about 80% of people’s water comes from drinks and 20% from food. The figure this calculator gives is a total of that kind. It is not glasses of plain water on top of everything else.
- Can you drink too much water?
- Yes, though it is rare. The National Academies set no upper limit for water but noted that some athletes in strenuous activity occasionally drink amounts that can be life-threatening. Do not treat the calculator’s figure as a target to beat.
- How much more water do you need when pregnant or breastfeeding?
- This calculator adds 0.3 L a day for pregnancy and 1.1 L for breastfeeding. Those are the gaps between the National Academies Adequate Intakes for total water: 2.7 L for women aged 19 to 30, 3.0 L in pregnancy and 3.8 L in lactation. At 70 kg with 30 minutes of activity the result goes from 2.56 L to 2.86 L or 3.66 L. Ask your doctor or midwife what suits you.
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