Thirst, pale yellow urine and how you feel are good day-to-day guides. Drink more when you sweat a lot, are ill with fever or vomiting, or are at altitude.
How the water intake calculator works
WaterIntakeCalc starts from 35 ml of fluid per kilogram of body weight a day, the upper end of the 30–35 ml/kg guidance often used by dietitians, which works out to just over half an ounce per pound. It then adds 355 ml (12 fl oz) for every 30 minutes of exercise, 500 ml for a hot or humid day, 300 ml during pregnancy and 700 ml while breastfeeding. The total is shown in fluid ounces, litres, 8-ounce cups and 16.9-ounce (500 ml) bottles, next to the US National Academies reference intake for comparison. Water, milk, tea, coffee and other drinks all count; watery foods such as fruit, vegetables and soup provide about a fifth of daily water on top.
Water intake chart by body weight
| Weight | No exercise | 30 min exercise | 60 min exercise | Litres (no exercise) |
|---|---|---|---|---|
| 100 lb (45 kg) | 54 fl oz | 66 fl oz | 78 fl oz | 1.6 L |
| 120 lb (54 kg) | 64 fl oz | 76 fl oz | 88 fl oz | 1.9 L |
| 140 lb (64 kg) | 75 fl oz | 87 fl oz | 99 fl oz | 2.2 L |
| 160 lb (73 kg) | 86 fl oz | 98 fl oz | 110 fl oz | 2.5 L |
| 180 lb (82 kg) | 97 fl oz | 109 fl oz | 121 fl oz | 2.9 L |
| 200 lb (91 kg) | 107 fl oz | 119 fl oz | 131 fl oz | 3.2 L |
| 220 lb (100 kg) | 118 fl oz | 130 fl oz | 142 fl oz | 3.5 L |
| 250 lb (113 kg) | 134 fl oz | 146 fl oz | 158 fl oz | 4 L |
| 300 lb (136 kg) | 161 fl oz | 173 fl oz | 185 fl oz | 4.8 L |
This is general information, not medical advice. Needs vary with health, medication, altitude and diet. People with kidney, heart or liver disease, or anyone told to restrict fluids, should follow their doctor’s advice. Drinking far more than you need in a short time can be dangerous.
Frequently asked questions
How much water should a woman drink a day?
The National Academies reference is about 2.7 L (91 fl oz) of total water a day, about 2.2 L (73 fl oz) of it from drinks.
How much water should a man drink a day?
About 3.7 L (125 fl oz) of total water a day, roughly 3 L (100 fl oz) of it from drinks.
Can I drink too much water?
Yes. Drinking several litres in a short time can dilute blood sodium (hyponatremia), which can be dangerous.
Is WaterIntakeCalc free?
Yes, with no sign-up or ads, and your numbers stay in your browser.
Is this medical advice?
No. It is a general estimate. If you have a health condition or have been told to limit fluids, follow your doctor’s advice.