Can you help me calculate my sweat loss?

Calculating sweat loss

Runners should consider rehydration and replenishment an individualised process after training. Every runner loses fluid and electrolytes differently. Some people sweat a lot of salt and others don’t. Unfortunately, this process can be difficult to optimise, as there is a small line for too little and too much. Too much may upset your stomach, too little may cause dehydration. What we can assure you is all of these will reduce your performance and recovery if not optimised. Focus should be made on consuming the right amount and kind of fluids.


As the process is so individualised we highly recommend you seek the expertise of Lisa Middleton, The Stride’s sports dietician.  

Runners must remember that temperature, humidity, and environmental factors will affect their sweat rate in addition to intensity and duration. Many experts suggest you should drink to thirst. However, heavy sweaters may not keep up with their sweat rate. So the question remains as to how best to monitor fluid loss.

In order to rehydrate effectively following a session, runners must estimate the amount of sweat lost during the run. Calculating your fluid loss in any given temperature and humidity is relatively simple if you have access to scales and create a reference chart.   Runners must take a measure of your body weight prior and following your run. This is best done nude as your clothing will store fluids as they absorb sweat. Measuring the change of weight of your clothing does not offer the best estimate of fluid loss, as sweat may be lost to other factors (i.e. Evaporation). In addition you need to note the duration and distance of the session and the amount of other fluid consumed or excreted.

The Stride recommends that you trial the calculator a number times in different temperatures and record your results. This will help you to develop a quick and easy to use reference chart. We also recommend that you record your perceived hydration and readiness following rehydration as each athlete responds differently. As such it is best for you to understand how you respond. This information with help you to know how quickly your body can get the fluids back in and help you avoid dehydration, over-hydration and stomach cramps.

Generalised Tips:

  • DURING exercise we recommend aiming to replace 80% of estimated fluid losses
  • For RECOVERY the goal is to consume 1.5 x the amount lost
  • When consuming fluid 250ml per 15 minutes for optimised rehydration (as the body can only absorb certain amounts at a particular time)


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