Staying hydrated can make or break your performance on the run. Learn how to calculate your fluid and electrolyte needs by following the steps below.
Calculating Your Sweat Rate
Calculating your sweat rate will help you learn how much fluid you lose per hour from sweat while exercising. You can use this data to help you determine how many fluids to consume on the run to avoid dehydration.
Step 1: Go for a run
- Use the restroom before you begin your run
- Weigh yourself pre-run in the nude (clothes can hold onto sweat and lead to inaccurate results)
- Run for 1 hour and avoid using the restroom
- Log how many oz of fluid you consumed on the run
- Towel off any excess sweat, then weigh yourself immediately post-run in the nude
- Pre-run weight: 150 lbs
- Fluids consumed: 8 oz
- Post-run weight: 149 lbs
Step 2: Calculations
Use the following formula to calculate your sweat rate.
- Subtract the post-run weight from the pre-run weight
- Convert lbs to oz
- Add the fluids consumed
- 150 lbs - 149 lbs
- 1 lb = 16 oz
- 16 oz + 8 oz = 24 oz lost/hour
Once you know how much fluid needs to be replaced per hour, divide this number by 4 to break the hour into 15-minute increments. Aiming to drink fluids every 15 minutes will help you sip your fluids gradually instead of chugging them all at once.
- 24 oz / 4 = 6 oz should be consumed/15 minutes
Calculating Your Electrolyte Needs
For runs that last over an hour, you'll want to add a source of electrolytes (particularly sodium). Calculating your exact sodium losses are a little more tricky than fluids, but the following guidelines are a good place to start.
Average sweaters need about 400-500 mg/L. Heavy, salty sweaters need more, with about 700 mg sodium per L of fluid consumed. If you often finish a run with salt granules or a while film on your skin/clothes, this is a good indication that you are a salty sweater. Light sweaters may need less, or close to 300 mg.
You can use your sweat rate to determine how many mg of sodium to consume on the run.
Step 1. Convert oz to L
Sweat rate is often calculated in oz. There are ~34 oz in 1 L. If you lose more or less sweat than 34 oz in an hour, you'll want to convert your sweat rate into L.
- 24 oz = 7/10 or 70% of 34 oz or 1 L
Step 2. Apply conversion to sodium range.
After selecting your sodium range (average, heavy, or light), apply the conversion to determine how many mg you'll need per hour.
- Runner is an average sweater (400-500 mg/L)
- 70% of 500 mg is 350 mg
- Runner should aim for about 350 mg of sodium/hour
Here are some popular products and their sodium content/serving.
- Gatorade Thirst Quencher = 160 mg sodium per 12 oz
- Gatorade Endurance = 300 mg sodium per 12 oz
- Powerade = 150 mg sodium per 12 oz
- Liquid IV = 500 mg per packet
- Nuun Sport = 300 mg per tablet
- Gu Energy Gel = 55 mg per packet
- Rold Gold Mini Pretzels = 450 mg per serving
Note: Your hydration needs will change in different climates. You may sweat more on a hot, humid day vs a cold, rainy one. This is why we recommend calculating your sweat rate at several points throughout the year in different climates to learn more about your hydration needs.