Calculate Your Sweat Rate to Formulate a Hydration Strategy

When it comes to performance you’ve probably heard that staying hydrated is super important, but how much do you actually need to drink? The answer lies in your sweat rate.

In simple terms sweat rate is the amount of fluid your body loses through sweating during exercise. Everyone’s sweat rate is different and can vary depending on the weather, intensity of the activity, clothing, and even fitness level. Calculating your sweat rate allows you to personalise your hydration strategy and get the most out of your performance.

The risk of not replacing fluid lost in sweat is dehydration - leading to fatigue, cramping, decreased performance and eventually exhaustion. On the flip side, drinking too much can dilute your blood sodium levels, which comes with its own set of problems in the potentially fatal hyponatraemia.

So how do you find your sweat rate?

To calculate your sweat rate you'll need:

• Scales in a private area to undress completely
• Towel
• Timer
• Drink bottle with hydration
• A toilet stop before you begin 

Instructions:

• Weigh yourself (nude) before exercise. Record your weight in kilograms (kg).
• Exercise for 60 minutes at the intensity you typically train or race at. Try to do this in similar conditions (temperature, clothing) to your usual environment.
• Keep track of how much you drink during the session in millilitres (mL).
• Weigh yourself again (nude) immediately after exercise
• Towel off sweat before stepping on the scale again, to get a more accurate reading.
• Note any toilet visits—ideally, avoid going during the session, as it complicates the calculation. 

The Sweat Rate Equation:
Sweat Rate (L/hr) = (Pre-Exercise Weight – Post-Exercise Weight [kg]) + Fluid Consumed (L) 

For example:

• Pre-exercise weight: 70.0 kg
• Post-exercise weight: 69.2 kg
• Fluid consumed: 500 mL (0.5 L) 
• Sweat loss = 0.8 kg Sweat rate = 0.8 kg + 0.5 L = 1.3 L/hour
  (Remember 1 kg weight loss equals approximately 1 litre of fluid lost) 

Once you know your sweat rate, you can tailor your hydration before, during, and after training. The goal during exercise isn’t to replace every drop, but to stay within about 2% of your starting body weight to maintain performance. For the example above (1.3 L/hour sweat rate), aiming to drink 700–900 mL/hour during similar sessions would be a smart starting point. 

An effective strategy is to start sipping early on and continue consistently through the session. Don’t forget electrolytes! When you sweat, you're not just losing water - you’re also losing sodium and other key electrolytes. If you're a heavy or salty sweater (you see salt crust on your skin or clothes), it’s worth considering additional sodium  (PURE Electrolyte Capsules or Race Fuel), especially for sessions longer than 90 minutes or in hot conditions.