Water Intake Calculator

"Drink eight glasses of water a day" is easy to remember, but it's also a rough average that ignores how much your actual needs vary by body size, activity level, and climate. This calculator starts from a more personalized baseline and adjusts it for the two factors that move the needle the most.

The starting point is a common rule of thumb: about half your body weight in pounds, expressed in ounces of water per day. A 160-pound person would start at roughly 80 ounces, or about 10 cups, before any adjustments. From there, the calculator scales that baseline up based on activity level, since exercise increases water loss through sweat and faster breathing, and climate, since hot or humid conditions increase fluid loss even without exercise, through sweat you may not fully notice.

These adjustments are intentionally general rather than tied to a specific number of exercise minutes or a precise temperature, since most people don't track their day in that much detail. Picking "active" if you exercise most days, or "hot" if you live somewhere with a hot summer or a warm climate year-round, gets you a reasonably tailored estimate without requiring a log of your workouts.

Keep in mind this number is a general target, not counting only plain water — beverages like tea, coffee, and milk, along with water-rich foods such as fruits and vegetables, all count toward daily fluid intake too. And certain conditions, including pregnancy, breastfeeding, illness with fever, or specific medical conditions like kidney or heart disease, can shift fluid needs in ways this calculator doesn't account for, so check with a doctor if you have any of those factors.