How to Calculate Your Sweat Rate
Calculating the amount of fluid we need as individuals can often be a tricky proposition. If you sweat 1/100th as much as I do then you likely need to know what you’re losing and what you need to take in to replace it during activity. If you don’t, your body can go into systematic shutdown to preserve itself. I’m by no means saying that sweating is a bad thing, you just need to know how it’s affecting your body (I once lost 11 lbs. during a particularly hot and long bike ride).
Below is a step-by-step formula for figuring out your own sweat rate and therefore, your hydration needs from Infinit Nutrition.
How to calculate your sweat rate:
The goal is to see exactly how much dehydration you incur during your workout and in turn,
determine your hourly fluid replacement (how much you need to drink). When you are done
with this homework, you will have a hydration target that you can use in both training and
1. Empty you bladder and record you weight (nude or swim suit)
2. Pre-exercise weight = ___________ lbs.(A)
3. Do your usual workout, and drink like you normally would.
4. Record the approximate volume of fluid consumed during exercise.
How much you drank = ___________ fluid ounces (E)
5. Towel dry, empty your bladder and then record your weight (nude or swim suit).
Post-exercise weight = ___________ lbs.(B)
6. Subtract your post-exercise weight from your pre-exercise weight to get the number of
pounds you lost during exercise.
Weight lost = _____lbs.(A) – ______lbs(B) = ________lbs.(C)
7. To find out how many fluid ounces of water you have lost,
multiply pounds x 16 _____lbs(C) x 16 = ________ fluid ounces of water you lost during
8. To determine hourly fluid replacement needs, add number of fluid ounces you lost during
exercise (D) to the number of fluid ounces you consumed during exercise (E) and divide by
total number of hours spent training.
(_____fluid ounces (D) + ___fluid ounces (E)) ÷ ___hours =_____fluid ounces needed each hour
Conditions that will increase sweat rate include heat, humidity, and elevated heart rate (high
intensity training). Athletes should measure sweat rate across several workouts to determine
their fluid replacement needs in various environmental conditions.
On race day, based on the forecast, the athlete than can go back to their log and know
exactly what fluid they need to plan on ingesting to prevent performance declines associated
with dehydration. Deaths have occurred when the air temperature was less than 75 degrees
F (24 degrees C) but the relative humidity was above 95%. Humidity levels over 75% will
contribute to an increased risk of heat injury.
*Note that a factor of 1.2-1.6 can be multiplied to hourly replacement needs when heat &
humidity (>75%) are extreme.
This is a key component to any athletes performance.