Calculating Your Hydration Needs During a Race

Runner hydrating during a long distance run

Why is Hydration Essential for Running?


Hydration is a key factor in running performance and recovery. A water loss of just 2% of body weight can lead to a significant decrease in performance, an increased heart rate, and a heightened perception of exertion.

Drinking enough helps you:
✔ Maintain a stable body temperature
✔ Delay muscle fatigue
✔ Avoid cramps and digestive disorders
✔ Optimize post-race recovery

Our hydration calculator helps you estimate how much water to consume before, during, and after your run, based on several individual parameters.

How to Calculate Your Hydration Needs While Running?


Ideal hydration depends on several factors:

Your weight: The heavier you are, the greater your water needs.
Race distance and duration: A marathon requires a more structured hydration plan than a 10K.
Intensity of effort: The faster you run, the more you sweat.
Temperature and humidity: Perspiration increases with heat and humidity.

General recommendation: On average, it is recommended to drink 400 to 800 ml of water per hour of running, but this figure can vary depending on conditions and individuals.

Use our interactive tool to find out your exact needs!

Comparison between hydration with and without electrolytes

Using the Hydration Calculator


Enter your parameters for a personalized estimate:


Indicate your weight
Select the distance of your race (5 km, 10 km, half-marathon, marathon, ultra-trail, etc.)
Enter the outside temperature

The tool will provide you with an accurate estimate of your hydration needs before, during and after the race.

Example of possible results:
• 10 km at 20°C: approximately 500 ml to 700 ml of water recommended.
• Marathon in hot climate (25°C and above): up to 1 liter per hour may be necessary.

Note: Excessive hydration can lead to hyponatremia (dilution of sodium in the blood), hence the importance of a good balance between water and electrolytes.
However, this calculation is theoretical and should only be used as an estimate. You should also listen to your body because we are all different and drinking a little more is beneficial in most cases, especially if you feel the need.

Hydration and Electrolyte Intake: Essential for Running?


Drinking water alone isn't always enough. When you sweat, you also lose electrolytes (sodium, potassium, magnesium), which are essential for fluid and muscle balance.

- Short runs (<1 hour): Water alone may be sufficient.
- Long runs (>1h): Add electrolytes or isotonic drinks to avoid cramps and dehydration.

Test your hydration plan in training! Every runner has different needs, and it's crucial to test your hydration in real-life conditions before a race.
Hydration needs table according to duration and temperature

Frequently Asked Questions about Hydration While Running


1. Should you drink before a race?


Yes, start hydrating properly 24 to 48 hours before a race. On race day, drink 500 ml of water about 1 to 2 hours before the start.

2. How much should I drink during the race?


It depends on your sweating and the weather conditions. Generally, a sip every 15 to 20 minutes will keep you well hydrated.

3. Can you drink too much while running?


Yes, excess water without electrolytes can cause hyponatremia, a dangerous imbalance of sodium in the blood.

4. What drink should you choose for a long run?


An isotonic drink containing electrolytes is ideal for replacing lost minerals.

Optimize Your Hydration Strategy with Our Other Tools!


Also discover:
Optimizing your refueling during the race (calculating carbohydrate intake)
Pace-speed converter in racing

Try our calculator and stay well hydrated on your next run!
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Guide d'hydratation

Résultat :

Avant la course : - ml

Pendant la course : - ml

Après la course : - ml

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