Water intake calculator
Find your daily hydration goal based on your body weight, activity level, and climate.
How daily water intake is calculated
This calculator uses the body-weight method: Water (ml) = Weight (kg) × 35 ml. An 80 kg person needs approximately 2,800 ml (2.8 litres) per day under normal conditions. For imperial: multiply weight in lbs by 0.5 to get ounces, or weight in lbs × 67 ml.
The 35 ml/kg baseline applies to a sedentary adult in a temperate climate. Exercise increases needs significantly: add approximately 500–750 ml for every hour of moderate exercise, more in hot weather or at high altitude. Total water intake includes all beverages — tea, coffee, milk, and juice count — plus water in solid food (typically 20% of total intake). Plain water remains the best source: it has no calories, no caffeine, and is immediately available. Thirst is generally a reliable indicator of hydration in healthy adults, but the elderly often have a blunted thirst response and should monitor intake more deliberately.