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How to calculate your sweat rate

November 11, 2019 2 min read

How to calculate your sweat rate

We get lots of questions from customers and athletes asking how much they should hydrate during specific workouts. While you can rest assured that First Endurance's EFS Drink Mix comes with the absolute most electrolytes on the market of any similar in-class product, that info alone isn't enough to help you figure out how much you should be drinking during a workout or race. 

Enter sweat rate. Your sweat rate is unique to you - it won't be the same as your training partner's, and it also may change over time. Sweat rate helps you understand your body's unique hydration requirements by calculating how much fluid you lose when exercising. When you know how to prevent too much fluid loss -- and therefore, dehydration -- you're effectively setting yourself up for stronger workouts less damage to the body while doing what you love.

To accurately measure your sweat rate, do the following:

  • Do a warm-up to the point where you start sweating
  • Urinate if necessary
  • Weigh yourself on an accurate scale (no clothing is best)
  • Work out for a specific amount of time (1 hour easiest, but 30 minutes can work if you simply multiply your end sweat rate by two, giving you your sweat rate per hour)
  • Drink a measured amount of your EFS Drink Mix or EFS Pro during the workout
  • Do not urinate during the workout
  • Weigh yourself again wearing EXACTLY what you wore during the initial weighing
  • Enter data into the table below

Sweat Rate Calculator:
This works best if converted into kilograms (kg) and milliliters (mL)


A. Body Weight pre‐exercise                      [lb/2.2 = kg]
B. Body Weight post‐exercise                      [lb/2.2 = kg]
C. Change in Body Weight                      grams [kg x 1000 = g]


D. Volume of fluid consumed                      mL [oz x 30 = mL]
E. Sweat Loss                      mL [oz x 30 = mL]

(C + D)

F. Exercise time                      [min or hr]
G. Sweat Rate                      [mL/min or mL/hr]



To convert Sweat Rate (G) back into ounces: G/30 = oz

The final number (G) is your sweat rate, or the amount of fluid that you lose through sweat during a specific amount of exercise (usually expressed per 1-hour). This should help you determine the amount of fluid you should be drinking during and after your workouts.

A key point to remember: sweat rate can vary during different climates. It's important to re-test in very hot or very cold climates. To that point, you should most definitely remember your sweat rate in the winter because even when it's cold, you're still sweating!

Happy training.


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