Hydration Rate Calculator Formula

Understand the math behind the hydration rate calculator. Each variable explained with a worked example.

Use the Hydration Rate Calculator

Formulas Used

Sweat Rate

sweat_rate_oz_hr = round(sweat_loss_oz / (exercise_minutes / 60) * 10) / 10

Sweat Rate (mL/hr)

sweat_rate_ml_hr = round(sweat_loss_oz * 29.574 / (exercise_minutes / 60))

Dehydration Level

dehydration_pct = round(weight_loss_lbs / pre_weight_lbs * 10000) / 100

Target Fluid Intake

fluid_target_oz_hr = round(sweat_loss_oz / (exercise_minutes / 60) * 0.8 * 10) / 10

Variables

VariableDescriptionDefault
pre_weight_lbsPre-Exercise Weight(lbs)160
post_weight_lbsPost-Exercise Weight(lbs)158
fluid_consumed_ozFluid Consumed During Exercise(oz)16
exercise_minutesExercise Duration(min)60
weight_loss_lbsDerived value= pre_weight_lbs - post_weight_lbscalculated
sweat_loss_ozDerived value= weight_loss_lbs * 16 + fluid_consumed_ozcalculated

How It Works

How Sweat Rate Is Calculated

Formula

Sweat Loss (oz) = Weight Lost (lbs) x 16 + Fluid Consumed (oz)

Sweat Rate = Sweat Loss / Exercise Duration (hours)

Each pound of weight lost during exercise represents about 16 oz (473 mL) of sweat.

Hydration Guidelines

  • Replace 80% of sweat losses during exercise.
  • Dehydration above 2% of body weight impairs performance.
  • Dehydration above 4% can be dangerous.

    • Factors Affecting Sweat Rate

  • Temperature and humidity
  • Exercise intensity
  • Body size
  • Fitness level (fitter athletes sweat more efficiently)
  • Genetics

    • Worked Example

    Pre-exercise: 160 lbs. Post-exercise: 158 lbs. Drank 16 oz during 60 minutes.

    pre_weight_lbs = 160post_weight_lbs = 158fluid_consumed_oz = 16exercise_minutes = 60
    1. 01Weight lost = 160 - 158 = 2 lbs.
    2. 02Sweat loss = 2 x 16 + 16 = 48 oz.
    3. 03Sweat rate = 48 / 1 hr = 48 oz/hr (1420 mL/hr).
    4. 04Dehydration = 2 / 160 x 100 = 1.25%.
    5. 05Target fluid intake = 48 x 0.8 = 38.4 oz/hr.

    Ready to run the numbers?

    Open Hydration Rate Calculator