How much water should you drink a day? Enter your body weight, how many minutes you exercise on a typical day, and whether the weather is hot or humid. The calculator gives a daily target in fluid ounces and liters, then breaks it into 8-oz glasses, standard 16.9-oz bottles and a per-hour amount so it is easy to spread through the day. Use the toggle to switch between US units and metric. The result is a rule-of-thumb estimate for healthy adults: thirst, pale-yellow urine and your doctor’s advice matter more than any single number.
How it works: base = body weight in pounds × 0.5 fl oz (about 33 ml per kg), plus 12 fl oz (355 ml) for every 30 minutes of exercise and 16 fl oz (about 0.5 L) for hot or humid weather. This is a popular rule of thumb, not a medical standard — for comparison, the US National Academies set adequate total water (drinks plus food) at about 3.7 L a day for men and 2.7 L for women. If you are pregnant, breastfeeding, have kidney or heart problems, or have been told to limit fluids, follow your doctor’s advice instead.