Water Intake During Exercise Calculator

About this calculator

Fluid intake during exercise is typically estimated from body weight, workout duration, and exercise intensity, since sweat rate (and therefore fluid loss) scales with all three — a heavier person exercising harder for longer loses proportionally more fluid through sweat. Sports-medicine guidance, including position stands from the American College of Sports Medicine (ACSM), generally recommends replacing fluids at a rate that limits body-weight loss during exercise to under about 2%, since dehydration beyond that threshold measurably impairs endurance performance, thermoregulation, and cognitive function.

Athletes, endurance runners, and cyclists use a hydration estimate like this to plan fluid intake before, during, and after a workout, since both under-hydrating (risking heat illness and performance decline) and over-hydrating (risking exercise-associated hyponatremia, a dangerous drop in blood sodium from drinking far more plain water than is lost in sweat) carry real risks — which is why guidance is framed as a personalized rate rather than a flat ‘8 glasses a day’ rule.

This calculator takes your body weight, workout duration, and intensity level, and returns an estimated fluid intake target for that session.