Fluid Loss Calculator

The Fluid Loss Calculator is an estimate of an athlete’s hourly sweat rate during exercise.

Please click here for instructions on how to use the Fluid Loss Calculator


This tool is useful for assessment of fluid losses during exercise based on changes in body weight. Sweat rate varies depending on factors such as environmental conditions, exercise type, exercise intensity, and clothing worn. Therefore, when used repeatedly for the same athlete this tool can be used to assess sweat rate in varying conditions. For the most accurate results, both fluid and food intake should be included in the calculations, along with any urine losses occurring during the test session. This tool will provide the practitioner with information to help the athlete develop a hydration strategy during exercise.

Time to complete: 5 minutes, plus time for data collection and exercise

Step 1: Pre-exercise fluid and food weigh-in.

  • Fluid and/or food should be consumed as desired by the athlete during the test; however, you will need to track what is put into the body.
  • If a food scale is available, record beginning weight for any food or beverage that might be consumed in grams.
  • If a food/beverage scale is not available, record the volume or weight of the food or beverage as noted on its container (For example: 20 oz of fluid or nutrition bar weight of 720 grams).
  • If an athlete will not consume food or fluid during exercise, enter -0- into the calculator.
Note: for accurate results it’s important the athlete only consume pre-weighed fluid/foods, that he/she does not share fluid/food during the test, and that any pre-weighted fluid/food is actually consumed – do not rinse the mouth and spit.

Step 2: Pre-exercise weigh-in.

  • Obtain a nude body weight. If a nude body weight is not practical, then have the athlete weigh in as little clothing as possible. Be sure to obtain the weight before any tape, wraps, etc. are applied to the athlete, and after the athlete urinates.
  • After a pre-exercise weight is recorded, the athlete should only consume his/her pre-weighed fluid/food.
Note: the more sensitive the measurement, the better. Example: 150.4 lbs will give you more accurate data than 150 lbs.

Step 3: Exercise

  • Record the duration of the exercise session to the nearest minute. Include the warm-up and cool-down as sweat loss can occur during this part of exercise.
  • Consume pre-weighed fluid/food as desired.
Note: for the most accurate sweat rate, any urine loss that may occur during exercise should also be recorded. This can be obtained by having the athlete collect urine using a pre-weighed container and weighing on a food/beverage scale. This calculator will calculate sweat rate with or without input of urine losses.

Step 4: Post-exercise weigh-out.

  • The athlete should use a towel to remove as much excess sweat as possible. A second body weight should be obtained wearing the same clothing as pre-exercise. Remember to remove any tape, wraps, etc. before recording the weight.
  • If a food scale is available, record ending weight for any remaining beverage and food in grams. Otherwise, record an estimation of the volume or weight of the fluid/food remaining as noted on its container.
  • If an athlete did not consume food or fluid during exercise, enter -0- into the calculator.

Step 6: Enter all values into the calculator