Sweat Rate Calculator - Understanding your sweat rate is a key part of staying properly hydrated during training and racing. Testing your sweat rate regularly helps you build an accurate picture of how much fluid your body needs under different conditions and intensities. To get the most reliable results, weigh yourself naked before and after a session—after briefly drying off—so you can track your fluid loss. Some degree of dehydration is normal, especially during longer or hotter sessions, but recent research shows that losing more than 4% of your body mass can lead to a noticeable drop in performance. Staying below that threshold is generally safe and allows you to perform at your best.