Race Time Predictor

Predict your race finish time for any distance based on a recent race result using the Riegel formula.

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miles
min
miles

Predicted Minutes

55 min

Predicted Hours1 hr
Predicted Seconds11 sec
Predicted Pace8.79 min/mile

Predicted Minutes vs Known Race Time

View formula & how it works →

How the Riegel Race Prediction Formula Works

The Riegel formula predicts race times across distances based on a known performance.

Formula

T2 = T1 x (D2 / D1) ^ 1.06

Where:

  • T1 = Known race time
  • D1 = Known race distance
  • D2 = Target race distance
  • 1.06 = Fatigue exponent

    • The formula works best for distances between 1500 m and the marathon, assuming similar fitness and training for both distances.

    Example Calculation

    You ran a 5K (3.1 miles) in 25 minutes and want to predict your half marathon time.

    1. 01Distance ratio = 13.1 / 3.1 = 4.2258
    2. 02Fatigue factor = 4.2258 ^ 1.06 = 4.6013
    3. 03Predicted time = 25 * 4.6013 = 115.03 minutes
    4. 04That is 1 hour, 55 minutes, and 2 seconds
    5. 05Predicted pace = 115.03 / 13.1 = 8.78 min/mile

    Frequently Asked Questions

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