Sweat Rate Calculator
Knowing your personal sweat rate is one of the most practical steps you can take to optimise hydration during training and competition. Sweat rates vary widely between individuals, ranging from under 0.5 litres per hour for sedentary individuals in cool conditions to over 3 litres per hour for athletes in hot climates. The standard field method involves weighing yourself before and after a measured exercise session, accounting for any fluid you drank. Each kilogram of weight lost corresponds to approximately 1 litre of sweat lost. This calculator performs those conversions for you and outputs your sweat rate in litres per hour, total fluid lost, and the recommended rehydration volume based on American College of Sports Medicine (ACSM) guidelines.
Sweat rate formula
Sweat Loss (L) = (Pre-weight kg - Post-weight kg) + Fluid Intake (L)
Sweat Rate (L/hr) = Sweat Loss / (Duration min / 60)
Rehydration Target (L) = Sweat Loss x 1.5
The 1.5 multiplier for rehydration is based on ACSM guidelines to account for ongoing urine losses during recovery.
Sweat rate: frequently asked questions
How do I measure my sweat rate?
Weigh yourself (nude, dry) immediately before exercise and again immediately after (nude, dry after towelling off). Note any fluid you drank during exercise. Sweat Rate (L/hr) = (Pre-weight - Post-weight + Fluid intake in kg) / Exercise duration in hours.
What is a typical sweat rate?
Average sweat rates range from 0.5 to 2.0 litres per hour depending on exercise intensity, heat, humidity, fitness level, and individual variation. Acclimatised endurance athletes in the heat can lose more than 3 litres per hour.
How much fluid should I drink to replace sweat loss?
The American College of Sports Medicine recommends drinking enough to replace 150% of fluid lost during exercise in the recovery period (i.e., 1.5 litres per 1 kg lost). During exercise, aim to drink regularly to limit body weight loss to no more than 2%.
Why does body weight change during exercise?
Most acute body weight change during exercise reflects fluid loss through sweat and respiration (and a small amount from fuel oxidation). Each kilogram of weight lost represents approximately 1 litre of fluid deficit, assuming no food intake.
Should I use sports drinks to replace sweat loss?
For exercise lasting more than 60-90 minutes, sports drinks containing electrolytes (sodium, potassium) help replace minerals lost in sweat and stimulate thirst. For shorter sessions, water is usually sufficient. The sodium content helps retain fluid and stimulate rehydration.
Official sources
- American College of Sports Medicine: Exercise and Fluid Replacement Position Stand.
- National Athletic Trainers' Association: Fluid Replacement Guidelines.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.