Key Takeaways
- Predicts race times for any distance from a single race result using the Riegel formula (1981), the most widely validated race equivalency model.[1]
- Estimates your VDOT score — a single-number fitness index from the Daniels-Gilbert model that drives training pace calculations.[2]
- Provides 5 Daniels training pace zones (Easy, Marathon, Threshold, Interval, Repetition) in both min/mile and min/km.
- Works with any race distance from Mile to Marathon, plus custom distances.
The Riegel Formula
Peter Riegel's 1981 formula (T₂ = T₁ × (D₂/D₁)^1.06) predicts race times for different distances using the empirical finding that performance slows by approximately 6% each time the distance doubles. This 1.06 exponent has been validated across thousands of performances from 1500m to marathon.[1]
The formula works best when predicting within a 2–4x distance range (e.g., 5K to half marathon). Predictions for much longer distances (5K to marathon) may be optimistic for less-experienced runners who haven't developed the muscular endurance for longer efforts. For marathon-specific training, see our Hansons Marathon Training Calculator.
Understanding VDOT
VDOT is Jack Daniels' single-number representation of your running fitness. While it correlates with VO2max, it also accounts for running economy and anaerobic contribution — two factors that lab VO2max testing alone doesn't capture.[2]
A higher VDOT means faster equivalent performance. Elite male distance runners typically score 70–85, elite females 60–75. Recreational runners usually fall between 25–50. Your VDOT drives the Daniels training pace system, ensuring your training paces match your current fitness level. For a direct VO2max estimate, try our VO2 Max Calculator.
Daniels Training Paces
Easy (E) Pace
60–65% of your training volume. Conversational pace (~66% VDOT) that builds aerobic base without accumulating fatigue. Most runners run their easy days too fast.
Marathon (M) Pace
Goal marathon race pace for marathon-specific long runs. Practice fueling and pacing at this effort for extended periods.
Threshold (T) Pace
“Comfortably hard” pace (~88% VDOT) sustained for 20–40 minutes. Develops ability to sustain faster paces over longer durations.
Interval (I) Pace
Hard 3–5 minute repeats that develop maximal aerobic power. Typically run as 800m–1200m intervals with equal recovery. Check your Running Pace Calculator for pace targets.
Repetition (R) Pace
Fast 200–400m reps focused on running economy and speed. Full recovery between reps to maintain form quality.
How to Use This Calculator
- Enter a recent race result — Use your most recent race time for the most accurate predictions.
- Review race predictions — Check predicted times for standard distances. These assume equal fitness development across distances.
- Note your VDOT — This single number represents your current running fitness level.
- Use the training paces — Structure your training week around these paces, with most volume at Easy pace.
- Retest after a training block — A new race or time trial will give you updated paces reflecting fitness gains.
Frequently Asked Questions
Sources & References
- Athletic records and human endurance. Riegel PS. American Scientist (1981)
- Oxygen Power: Performance Tables for Distance Runners. Daniels J, Gilbert J. Cortland, NY (1979)
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Disclaimer: This tool is for informational and personal journaling purposes only. Results are estimates based on published formulas and may vary based on individual factors such as genetics, training history, and measurement technique.