Sweat Rates: Weighing Your Way to a Drinks Plan
Two weigh-ins and a bottle count give a surprisingly useful number. This post explains the formula and how to use the rate.
What is the Sweat Rate Calculator?
Weigh yourself before and after exercise, add the fluid you drank, and divide by the hours to get a sweat rate in litres per hour. Enter those four figures and the tool does the division. It is an estimate for planning drinks, not medical advice, and large losses deserve a proper hydration plan.
How to use it
- Weigh yourself before and after exercise.
- Enter the fluid you drank and the duration.
- Click Calculate Sweat Rate.
Worked example
75 kg down to 74 kg with 0.5 litres drunk over 1 hour gives 1.5 litres lost, a sweat rate of 1.5 litres per hour.
Should I drink exactly my sweat rate?
Usually a little less during the session and the rest afterwards works better, since drinking at full sweat rate can upset the stomach.
Frequently asked questions
Why does weight loss equal fluid loss?
Over a single session, most of the weight change is fluid, though food, clothing, and bathroom breaks add small errors.
Does heat change the rate?
Yes, a lot. Re-measure in hot conditions rather than trusting a cool-weather rate.