A 170 lb adult who exercises 30 minutes a day comes out at about 103 fl oz (3.1 L), or roughly 13 cups.
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 I drink a day?
A common rule is about 30–35 ml per kg (around half an ounce per pound) of body weight, plus more for exercise and heat.
Does coffee count toward water intake?
Yes. Tea, coffee, milk and other drinks all count toward your fluid intake; caffeine’s mild diuretic effect is small for regular drinkers.
Is 8 glasses a day right?
Eight 8 oz glasses (64 oz, about 1.9 L) is a simple minimum for smaller adults; most people need more.
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.