Race comparison.
Feed in two-to-four race results, get your personal Riegel exponent. Discover whether you skew speed, endurance, or balanced — and how your fitted predictions differ from the textbook 1.06.
How this calculator works
- VDOT and equivalent training paces
VDOT is a single number that summarizes your aerobic fitness from a recent race performance. Daniels' tables map VDOT to equivalent times at every standard distance and to recommended paces for easy, marathon, threshold, interval, and repetition work. PaceCalc estimates VDOT from your inputs, then surfaces those equivalent paces.
Jack Daniels, Daniels' Running Formula, 3rd edition, Human Kinetics, 2013. Tables for VDOT and zone-based pacing.
- Riegel formula
The Riegel formula projects a finish time at one distance (T₂) from a known time at another (T₁) using T₂ = T₁ × (D₂/D₁)^1.06. The 1.06 exponent captures the typical fatigue curve for trained runners. PaceCalc uses 1.06 as the default; you can adjust the exponent on the race-predictor page if you fade harder than average.
R. H. Riegel, "Athletic Records and Human Endurance," American Scientist, vol. 69, no. 3, 1981, pp. 285–290.
- Equivalent-performance comparison uses VDOT to convert each race to a single fitness number, then compares. Results are most reliable when both races were within the same training cycle.
Frequently asked
- What is the Riegel exponent?
- The Riegel exponent (standard: 1.06) describes how performance declines as race distance increases. A personal exponent below 1.06 means you're relatively stronger at longer distances; above 1.06 means you're stronger at shorter distances.
- How many races do I need for accurate comparison?
- At least 2 races are required, but 3-4 across different distances gives much better results. Ideally, include a mix of short (5K/10K) and long (half/full marathon) distances.
- What does 'speed-biased' vs 'endurance-biased' mean?
- Speed-biased runners (exponent > 1.09) perform relatively better at shorter distances — their times drop off more than average as distance increases. Endurance-biased runners (exponent < 1.03) are the opposite.
- Why are my personal predictions different from standard ones?
- Standard predictions assume you're an 'average' runner in terms of speed vs endurance balance. Your personal exponent captures your unique profile, making predictions more accurate for your physiology.
- How can I use this information in training?
- If you're speed-biased, add more endurance-focused training to unlock longer distance potential. If endurance-biased, speed work could help you improve shorter race times. Target races at your strongest distance for PRs.