Water Intake Calculator
This water intake calculator shows how much water you should drink per day — in ounces, cups and liters — based on your body weight and how long you exercise.
Your numbers
Your result
Formula: Mifflin-St Jeor (1990). General fitness information, not medical advice.
How your water target is set
Bigger bodies hold and turn over more water, so the baseline here is 35 milliliters per kilogram of body weight — a widely used rule of thumb that lands near the familiar 8-cups advice for average adults and in the same ballpark as the U.S. National Academies' adequate-intake figures (about 3.7 L/day total fluid for men and 2.7 L for women, food included). Exercise adds sweat losses, so the calculator tacks on 350 ml for every 30 minutes of activity. Food already covers roughly 20% of your fluid needs, and coffee and tea count toward the total too. Treat the number as a general guideline, not medical advice — hot climates, pregnancy and some medical conditions change your needs.
Worked example. A 180 lb person is 180 ÷ 2.205 = 81.6 kg. Baseline water is 81.6 × 35 = 2,858 ml. Add one 30-minute workout (+350 ml) and the target is 3,208 ml — about 108 oz, 13.6 cups, or 3.2 liters across the day. Skip the workout and it drops to roughly 97 oz.
Daily water target by body weight and exercise
| Body weight | No exercise | 30 min/day | 60 min/day |
|---|---|---|---|
| 120 lb (54 kg) | 64 oz · 1.9 L | 76 oz · 2.3 L | 88 oz · 2.6 L |
| 150 lb (68 kg) | 81 oz · 2.4 L | 92 oz · 2.7 L | 104 oz · 3.1 L |
| 180 lb (82 kg) | 97 oz · 2.9 L | 108 oz · 3.2 L | 120 oz · 3.6 L |
| 210 lb (95 kg) | 113 oz · 3.3 L | 125 oz · 3.7 L | 136 oz · 4.0 L |
Baseline is 35 ml/kg plus 350 ml per 30 minutes of exercise; 1 cup = 8 oz. Food and other drinks contribute to this total. General hydration guidance, not medical advice.