Sweat Test

Estimating Your Sweat Rate: A Practical Guide for Endurance Athletes

Understanding your sweat rate is a valuable step toward refining your hydration strategy, both in training and on race day. Knowing how much you typically lose through sweating helps you determine what—and how much—you need to drink to replace fluids and electrolytes.

Sweat rate is highly individual. Some athletes naturally sweat more, while others sweat less, and it can vary significantly depending on conditions. Heavier or faster-moving athletes, or anyone training in warm environments, will usually experience higher sweat losses. Meanwhile, lighter athletes, those training at steadier intensities, or anyone working out in cooler weather, will often see lower rates.

Because of this variability, it’s worth measuring your sweat rate several times under different conditions. Doing so provides a clearer picture of what to expect. If you are planning hydration for a particular event, try to mimic expected temperatures using heating or air conditioning. It’s best to complete at least four practice sessions at your target race conditions to allow your body to adapt and respond similarly to how it will on race day.

Below is a simple step-by-step process for collecting the data you need, followed by guidance on using the results.

What You’ll Need

• A reliable, accurate set of weighing scales

• A dry towel

• A drink bottle with a known volume (remember, 1 litre ≈ 1 kg)

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How to Calculate Sweat Rate

1. Use the loo before starting. Any mid-test toilet break will skew your numbers. Record your body weight, ideally without clothing, for accuracy.

2. Complete your training session. To make the test specific to your target race, aim to mimic the expected conditions using heating or air conditioning. Ride or run at your intended race pace for at least one hour.

3. Note your fluid intake. For example, a 750 ml bottle equals 0.75 kg of fluid.

4. Weigh yourself again post-session. Towel off thoroughly and weigh yourself without clothing, as the kit will hold sweat and distort the result.

5. Calculate your sweat loss. Use your pre- and post-exercise weight, along with the total fluid consumed, to determine weight lost during the session. You can plug this information into the sweat-rate-calculator for accuracy.

6. Review your sweat rate. You’ll now have a reliable estimate of how much fluid you lose per hour and an idea of how much to replace within the next two hours.

Salt & Electrolyte Considerations

Whilst this test can give you good insight into your fluid loss at a given intensity and temperature, it’s absolutely crucial to include some salt in your fluids. A generic, safe amount for most athletes is roughly ¼ to ½ of a level teaspoon of sea salt per litre of fluid.

Alongside working out your fluid loss, you can also estimate how “salty” a sweater you are. The ratio of salt to water in your sweat tends to remain fairly consistent, so once you know it, you can always add the correct amount of sodium. Here’s a helpful guideline based on how your clothing looks post-session:

• Sweating buckets – drenched and covered in white salt after a race or hard session over one hour: ~2000 mg sodium per litre or one teaspoon of salt.

• Pretty darn sweaty – still drenched, less white than the saltiest sweaters: ~1500 mg sodium per litre or ¾ teaspoon of salt.

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  Fairly sweaty – wet all over but not completely drenched: ~1000 mg sodium per litre or ½ teaspoon of salt.

• A bit sweaty – a sheen of sweat over the body: ~750 mg sodium per litre or 3/8 teaspoon of salt.

• Not sweaty – barely noticeable sweat: ~500 mg sodium per litre or 2/8 teaspoon of salt.

Dialling in hydration isn’t about perfection—it’s about learning how your body responds so you can race more comfortably, consistently, and with greater confidence. If you’d like help interpreting your results or building a hydration plan around your race goals, feel free to get in touch.

Happy triathlOn-ing!

Pete