Daily Water Target (Weight-Based) Calculator

About this calculator

One common rule of thumb for daily water intake scales the target to body weight: roughly 33 mL per kilogram of body weight per day (about half an ounce per pound), with an extra allowance added for exercise or heat exposure since sweating increases fluid loss. A 70 kg adult would land around 2.3 liters a day from this formula before any activity bonus.

This weight-based method is a commonly cited starting point in general wellness guidance, though it's a simplification — actual fluid needs also depend on climate, diet (fruits and vegetables contribute water too), and individual health conditions, and authoritative bodies like the National Academies express total water needs as a broader range rather than a single per-kilogram number. It's most useful as a rough daily target rather than a precise medical requirement, which is why it's commonly paired with a reminder that it isn't medical advice.

This calculator takes your body weight and any activity bonus and returns a daily water intake target.