Sweat Rate Calculator
Fluid lost per hour, from weight before and after.
Gaining weight during exercise means you are over-drinking. Exercise-associated hyponatraemia is rare but has caused deaths in endurance events.
Sweat rate
1500 ml/hour
1.4% of body weight lost
Under 2% loss is the usual target. For sessions under an hour, drinking to thirst is generally adequate.
How the Sweat Rate Calculator works
Sweat rate varies enormously — from under half a litre to well over two litres an hour depending on the person, the intensity and the weather. Generic hydration advice cannot account for that, but weighing yourself before and after a session can.
Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.
Frequently asked questions
How do I measure my sweat rate?
Weigh yourself nude before and after exercise, note any fluid you drank, and account for urine passed. Sweat loss = (weight before − weight after) + fluid consumed. One kilogram of weight lost is roughly one litre of sweat.
How much should I drink during exercise?
Enough to keep losses under about 2% of body weight, which is where performance begins to decline measurably. For most people during sessions under an hour, drinking to thirst is adequate; longer or hotter sessions benefit from a plan based on measured rate.
Can you drink too much during exercise?
Yes, and it is genuinely dangerous. Drinking beyond sweat losses can dilute blood sodium and cause exercise-associated hyponatraemia, which has caused deaths in endurance events. Gaining weight during exercise means you are over-drinking.
Do I need electrolytes or is water enough?
Water is fine for most sessions under about an hour. Beyond that, or in heat with heavy sweating, sodium replacement helps maintain fluid balance and reduces hyponatraemia risk. Sweat sodium concentration varies several-fold between individuals.