Sweat Rate Calculation

How much you sweat will determine how much you need to drink. And calculating it is much easier than you think.

The goal of drinking during exercise is to prevent significant dehydration and to enable peak performance. Your sweat rate determines your fluid requirements during exercise. And everyone sweats differently. Genetics, gender, training, and acclimatization all affect your sweat rate. In addition, the harder you work, the more you sweat. The hotter it is, the more you sweat. And other factors like humidity, sun, wind, and clothing will impact your sweat rate. We all know the heavy sweater who turns a training room into a swimming pool in less than an hour, and we all know the other person who hasn’t broken a sweat even after 1 hour of hard work!

The simplest case is measuring sweat rate when exercising without consuming any food or drink and without going to the bathroom. If you weigh yourself before and after your exercise, the difference in weight is primarily due to sweat loss.  Convert that to fluid volume and you have sweat loss (1kg = 1L). When you divide that sweat loss by the exercise time, you have sweat rate. If you consumed fluids or went to the bathroom, adjustments can be made to account for these.

For complete step-by-step instructions on how to measure your sweat rate and a handy spreadsheet to do the calculations for you, please reference the CORE Nutrition Planning article Sweat Rate Calculation (with Spreadsheet Calculator).

Measuring your sweat rate once does provide helpful information.  But measuring it multiple times under different conditions (different temperatures, different workout intensities, perhaps even running vs biking) will provide greater understanding of your sweat rate for easy cool workouts and hard, hot races. And, it will allow you to average out some of the measurement errors that may come from inaccuracy of your scale, temperature measurement, fluid intake measurement, etc.

Knowing your sweat rate is important. The more you measure, the more your knowledge will increase: a very literal example of knowledge is power.