Daily Water Target by Weight Calculator

About this calculator

A common rule-of-thumb for hydration used across fitness and nutrition apps scales daily water intake to body size: roughly 33 mL of water per kilogram of body weight per day, which lands in the same general range as other commonly cited guidelines like “half your body weight in ounces.” Larger bodies have more metabolically active tissue and a greater fluid volume to maintain, so their baseline needs are higher.

Because that weight-based baseline does not account for how much you sweat, this calculator adds an optional activity bonus on top of it for exercise or hot-weather exertion. The result is a starting estimate for daily fluid intake, not individualized medical guidance — actual needs vary with climate, health conditions, and diet, so this is not a substitute for advice from a doctor or dietitian.