Runner’s Tool Box: Race Conversion Calculator (Predicts Finish Times Based on Other Race Distances)

Posted by Filed Under: Tools for Runners


  • Enter a distance (a number) you have run recently.
  • Select kilometers or miles (1 mile = 1600 meters = 1.6 kilometers, etc.).
  • Enter the time it took you to run that distance.
  • Enter the distance (a number) you want a prediction for.
  • Select kilometers or miles for the race you want a prediction for.
  • Click on calculate.

I have run:


I want to know my predicted time for:

Predicted Time:

How does this get your predicted time? The formula used for this calculator was devised by Pete Riegel in the late 70s. It has withstood the test of time as a formula as accurate as any out there for running. In the early 80s, Riegel refined it for other sports for an article entitled “Athletic Records and Human Endurance” published in American Scientist.
Does credit for the code in this tool belong to you? We found this a few years ago and do not know where it came from so, if it is yours, please contact us so we can properly credit you.

About Mark Iocchelli

Also known as the "Running Blogfather", I'm a 40-something marathoner who has beaten stress fractures and terrible shin splints. Now I'm running double the mileage with no pain - and I'm getting faster. I love to talk about running form and Arthur Lydiard. I also enjoy taking photographs, have a beautiful (and very patient!) wife, and am the proud father of two crazy kids. Feel free to contact me if you have any questions or comments about the site.

  1. Bob on October 5th at 11:14 am

    If this calculator proves correct I will be doing backflips in Chicago. 😉

  2. Danielle in Iowa on October 5th at 11:32 am

    So here is something that has always made me curious with these calculators. I am running a half-marry in a week and if I put in my time based on my ten mile race a couple weeks ago I get 2:11. If I put in my marathon time from June (and I was in better shape at that point), I get 2:31.

    It seems like these calculators depend on a factor (runners world is something like t^1.06) to determine how much faster/slower you will run based on the decrease/increase in distance… That factor had to be figured out somehow (experimentally?) and I have always wondered if it is based on more finely tuned athletes who can haul ass in shorts distances and never bonk in long ones?

    Anyways, as much as I want them to be, these have never been good predictors for me!

  3. Blaine Moore (Run to Win) on October 5th at 12:42 pm

    I always use the McMillan Running Calculator for predictions. It combines a few of the tools that have been showing up here. I wrote about it at RTW last year.

  4. Kate Dugas on October 5th at 11:27 pm

    There are quite a few people talking about getting into running on this site:

    while a lot of them might not be doing the kind of running you folks are 😉 I bet they would really appreciate knowing about these tools.

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