About PacePercentile
How the calculator works, the formulas behind the results, and why we built this tool.
What Is PacePercentile?
PacePercentile.com is a free running calculator that helps runners convert between pace, speed, distance, and finish time. All calculations happen instantly in your browser — no data is sent to any server.
The site is built and maintained by the PacePercentile team — runners and data enthusiasts who care about making running tools that are fast, accurate, and free.
The site is part of the Percentile family of calculator tools, which also includes GrowthPercentile.com for pediatric growth charts.
How Pace Is Calculated
Pace is simply total time divided by total distance:
Pace = Time ÷ Distance
For example, if you run 5 kilometers in 25 minutes, your pace is 5:00 per kilometer (25 ÷ 5 = 5). To convert to miles, we use the conversion factor of 1 mile = 1.60934 km.
Race Time Predictions
Race equivalents use the Riegel formula, the most widely used race prediction model in distance running:
T2 = T1 × (D2 / D1)1.06
Where T1 is your known time for distance D1, and T2 is the predicted time for distance D2. The exponent 1.06 accounts for the natural slowdown as distance increases.
This formula was published by Peter Riegel in a 1977 article in Runner's World and has been validated across thousands of race results. It is used by Runner's World, Strava, and most running apps.
Limitations
- Most accurate between 1 mile and marathon distances for trained runners
- Less reliable for ultra distances (50K+) due to additional fatigue factors
- Assumes equal training specificity across distances
- Does not account for terrain, weather, altitude, or nutrition
Split Times
Split tables show your projected time at each kilometer or mile marker, assuming even pacing throughout the run. While most runners slow slightly in the second half of a race (positive splitting), an even-split strategy is generally the most efficient approach to race-day performance.
Privacy
All calculations happen entirely in your browser using JavaScript. PacePercentile.com does not collect, transmit, or store any personal data or running information. See our Privacy Policy for details.
Contact
Questions or feedback? Email [email protected]