Knowing Your Sweat Rate

Answering the question, "what is my sweat rate?" can be tricky. Although it can be calculated easy enough, there are so many variables that can affect it that it will not always be the same. It will change depending on the type and intensity of activity, temperature outside, genetics, humidity, and the type of clothing/equipment you are wearing. Being mindful with your hydration plan will help prevent some of the effects of dehydration and possible muscle cramping. 

An example of how much sweat rates can vary can be seen by looking at two tennis players.

Male 1: He is in his summer competition with an average sweat rate of 1.6 L per hour.
Male 2: He is also in his summer competition and is prone to muscle cramps. His sweat rate is 2.6 L per hour.

As you can see, most everything between these two males is the same (temperature outside, humidity, clothing) with the exception of their genetics. So it goes to show that you really need to pay attention to your body and how much YOU are sweating to estimate how much water you should be drinking. Not only are you losing fluid in your sweat, but also electrolytes. Sodium, in particular, is lost in sweat and even the rate of that is highly dependent on genetic factors. Some people are "salty" sweaters while others not. It may require adding in some electrolytes to your water or drinking a sports drink.

Reference:
Sawka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., & Stachenfeld, N. S. (2007). American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and science in sports and exercise, 39(2), 377-390.