Estimate how much water to drink per day from your body weight and exercise.
92
Liters per day
2.72
Cups per day
11.5
From body weight
80
87.0%From exercise
12
13.0%How much water should you drink each day? The answer is less straightforward than popular health advice suggests. A practical rule of thumb is to drink roughly half an ounce of water per pound of your body weight, then add extra fluid for any exercise you do. So a person weighing 160 pounds would start with 80 ounces as a baseline, then add about 12 ounces for every 30 minutes spent exercising. This method accounts for the fact that heavier bodies require more hydration to function, and that sweating during exercise depletes fluid faster. However, actual water needs shift with climate, diet, health conditions, and individual physiology - some people naturally retain water better, while others lose more through perspiration or urination. The formula here assumes average activity and normal health, and it works best as a number you nudge up or down rather than one you hit exactly. Many people drink more or less than this estimate and stay perfectly well. Thirst, urine color, and how you feel during and after exercise are better guides than any fixed number.
A 160-pound person exercising for 30 minutes per day should drink about 92 ounces daily. The baseline is 160 × 0.5 = 80 ounces, plus 12 ounces for the 30-minute workout, giving 92 ounces. In metric units, that is roughly 2.72 liters or about 11.5 cups.
A 70-kilogram person with no deliberate exercise needs about 77 ounces per day. Converting to pounds: 70 kg × 2.2 ≈ 154 pounds, so the baseline is 154 × 0.5 ≈ 77 ounces. No exercise bonus is added.
Is the "8 glasses of water a day" rule correct?
The 8×8 guideline (eight 8-ounce glasses = 64 ounces) is roughly equal to the baseline half-ounce-per-pound rule for someone weighing around 128 pounds. For lighter people, 64 ounces might be more than they need; for heavier people, it is often not enough. It is a memorable guideline but not personalized. This calculator adjusts for your actual body weight and exercise, making it more accurate for most individuals.
Does coffee or tea count toward my water intake?
Caffeinated drinks like coffee and tea do contribute to overall fluid intake, though caffeine has a mild diuretic effect that increases urination slightly. For most people, the fluid in these beverages counts roughly the same as water for hydration purposes. Sugary drinks and alcohol are a different story - they carry additional calories or metabolic effects that go beyond simple hydration.
Can you drink too much water?
Yes. Drinking excessive amounts of water in a short time can lead to hyponatremia - a dangerous drop in blood sodium that happens when water intake vastly outpaces the body's ability to excrete it. This is rare but serious, and it is another reason why a general estimate like this should never be treated as a rigid prescription. Listen to your thirst, monitor how you feel, and adjust if something does not feel right.