What formula does this tool use?

The tool uses Pete Riegel's formula: T2 = T1 × (D2/D1)^1.06. The exponent 1.06 accounts for the physiological fatigue that makes longer races disproportionately harder than simply scaling by distance.

How accurate are the predictions?

Riegel's formula is accurate for well-trained runners with consistent training. Results can vary by ±5–10% depending on your individual strengths (speed vs. endurance), course elevation, weather, and fueling strategy. Use predictions as a guide, not a guarantee.

Why does the formula favor shorter distances?

The exponent 1.06 means pace slows slightly as distance increases. This reflects real human physiology — you cannot maintain 5K race pace for a marathon. The formula captures this degradation mathematically.

Which distances are included?

The tool covers the four most common road race distances: 5K (3.107 miles), 10K (6.214 miles), half-marathon (13.109 miles), and marathon (26.219 miles).

Can I use a time from a non-standard distance?

Currently the tool requires an input from one of the four standard distances. For best accuracy, use a recent race time rather than a training run time.

Does fitness level affect accuracy?

Yes. Riegel's formula works best for aerobically trained runners. Beginners may find marathon predictions optimistic, since aerobic base affects how well pace transfers across distances.

Race Time Converter

Name: Race Time Converter
Availability: InStock
Author: Nham Vu

Enter a finish time for any standard race distance and instantly see predicted equivalent times for all other distances.

Your Known Race Time

Race Distance

Finish Time

Hours

Minutes

Seconds

Uses Pete Riegel's endurance formula: T2 = T1 × (D2/D1)^1.06

Predicted Times

Enter your race time on the left
and click Convert to see predictions.

Distance	Finish Time	Pace/mi	Pace/km

Based on your time. Predictions assume consistent aerobic fitness across distances.

Summary

Enter a finish time for any standard race distance and instantly see predicted equivalent times for all other distances.

How it works

Select the race distance for which you already have a finish time.
Enter your finish time in hours, minutes, and seconds.
The tool applies Pete Riegel's endurance formula to calculate predicted times for every other standard race distance.
Review your predicted times and per-mile / per-kilometer paces in the results table.
Use the results to set realistic goals for your next race.

Use cases

Predict a marathon finish time from a recent half-marathon result.
Determine a realistic 5K goal after completing a 10K race.
Compare training paces across all standard race distances.
Set time goals for your next race registration.
Evaluate fitness improvement by comparing predictions over time.
Plan race-day pacing strategy based on equivalent effort.

Frequently Asked Questions

Last updated: 2026-07-01 · Reviewed by Nham Vu