Calculate how much water you should drink daily based on weight and activity level.
Daily hydration needs based on your body and activity
This free calculator gives you instant, accurate results with no signup required. Use it to make smarter, more informed financial and life decisions.
Always double-check important financial decisions with a qualified professional. This calculator provides estimates for guidance purposes. Results may vary based on your specific circumstances.
The "8 glasses a day" rule is a oversimplified myth — actual water needs vary significantly based on body weight, activity level, climate, and even diet (foods with high water content count toward intake too).
A more personalized formula uses body weight as the baseline — roughly half your body weight in ounces for sedentary individuals, scaling up significantly for athletes and those in hot climates. A 200lb athletic person in a hot climate may need close to a gallon daily, while a sedentary 130lb person in a temperate climate may need far less than the "8 glasses" myth suggests.
Signs of adequate hydration are more reliable than rigid targets — pale yellow urine, rarely feeling thirsty, and stable energy levels are good indicators. Dark urine, frequent headaches, and fatigue can signal under-hydration even if you think you're drinking "enough."
Use the calculator above for a personalized daily target based on your weight, activity level and climate — then adjust based on how your body actually responds, since individual hydration needs vary more than generic advice accounts for.