PowerBar: Sports Nutrition and Training: Sweat Rate Calculator

Unreplaced fluid losses during extended workouts can compromise your athletic performance and pose health risks. Sports medicine authorities, including the American College of Sports Medicine, now recommend individualized hydration analysis so athletes can tailor their fluid intakes to sweat rates.

Staying within 2% of your pre-exercise body weight during training or competing, called your hydration zone, can help you maximize your athletic performance and prevent dehydration or overhydration. By consuming adequate fluids during exercise, you can be sure that you stay in your hydration zone.
An individualized hydration analysis involves determining your sweat rate based on a one-hour test workout:
Test yourself at an exercise intensity and in climate conditions similar to the conditions you expect to encounter in your training or upcoming event. Better yet, test yourself at different exercise intensities and in different climate conditions, and as your fitness level changes.
Repeat sweat rate testing under varying conditions will help you to better understand how your body responds to different conditions. This in turn will help you fine-tune your hydration plan for whatever you encounter during training and competing.