Hydration During Exercise: How Much Water and Electrolytes Do You Need?

By Lorayne Haye, M.S.C.N., CSNC

Proper hydration during exercise supports performance, endurance, recovery, and overall well-being. Many people ask how much water they should drink before, during, and after a workout, especially during longer sessions or in hot weather. While hydration needs vary from person to person, a simple formula can provide a practical starting point for estimating fluid intake during exercise.

How to Calculate Hydration During Exercise

One commonly used exercise hydration guideline is often referred to as the Galpin Equation. To estimate how much water to drink during exercise, divide your body weight in pounds by 30. The result is the approximate number of ounces of water to drink every 15 to 20 minutes during exercise. This serves as a general hydration guideline for workouts and can help answer the common question, “How much water should I drink while exercising?”

Example: If a person weighs 240 pounds, dividing 240 by 30 gives 8. That means they would aim to drink about 8 ounces of water every 15 to 20 minutes while exercising.

For a 2-hour workout (120 minutes), using 15-minute intervals, there are four 15-minute segments per hour. At 8 ounces per interval, this equals 32 ounces per hour.

Over the course of 2 hours of exercise, that totals 64 ounces of water.

It is also important to remember that hydration is not just about water intake. During longer or more intense workouts, the body loses electrolytes through sweat, including sodium and other minerals that help maintain fluid balance. In some cases, replacing fluids with added electrolytes may be helpful, especially during endurance exercise, hot weather workouts, or prolonged activity. The chart below can help you assess hydration status at a glance.

How to Measure Sweat Loss and Rehydrate After a Workout

1. Weigh yourself before exercise: Do so without clothing for the most accurate baseline measurement.

2. Exercise for a set period of time: Complete your planned workout or training session.

3. Weigh yourself again after exercise: Use the same conditions, if possible, to improve accuracy.

4. Calculate sweat loss: Subtract your post-workout weight from your pre-workout weight to estimate how much fluid you lost during exercise.

5. Rehydrate after exercise: Drink 16 to 24 ounces of fluid for every pound of body weight lost to support post-workout recovery and rehydration.

Note: Hydration needs can vary based on body size, sweat rate, exercise intensity, environment, and overall health. Use this formula as a practical guideline, and adjust based on how you feel and perform.

Disclaimer: This information is provided for educational purposes only and is not intended as medical advice. Individual hydration needs vary, so consult a qualified healthcare professional for personalized guidance.