What is your performance index?
If the world record is minutes and seconds (put in a 1 below to find out)
and your time was minutes and seconds,
your performance index is (copy this and paste below).

What is your equivalent performance?
If your performance index is , your:

women's indoor mile is :*
women's outdoor mile is :*
women's indoor 3k is :
women's track 5k is :
women's road 5k is :
women's road 5 mile is :
women's road 10k is :
women's half marathon is ::*
women's marathon is ::

men's indoor mile is :
men's indoor 3k is :
men's indoor 5k is :
men's road 5k is :
men's road 5 mile is :
men's half marathon is ::
men's marathon is ::
Sources for times: Track and Field News records (standard distances) and Athletics Weekly records (standard plus extra distances)

To compute the ratio of two times:
Numerator time: :
Denominator time: :
The ratio is .
The ratio of men's to women's world records is between 0.88 and 0.91.

FAQ: How does this work?
To get your "performance index," the world record for the event is divided by your time. To find an equivalent performance, divide the world record by your performance index.
Easy example: Suppose that you are male and you run a 4:08 marathon. The world record for the men's marathon is 2:04, so your performance index would be 2:04/4:08 = 0.5. To find an equivalent performance in the men's road 5k, divide the men's road 5k world record of 13:00 by your performance index of 0.5: 13:00/0.5 = 26:00.
Hard example: I just ran 10:07.56 for the women's indoor 3k. So I divide the women's indoor 3k world record of 8:23.72 by my time: 8:23.72/10:07.56 = 0.829. Now I want to know what an equivalent performance in the indoor mile is, so I divide the women's indoor mile record of 4:17.14 by my performance index: 4:17.14/0.829 = 5:10.2.

FAQ: Can I use this to predict future performances?
You can, and I do. However, a better question is whether it is accurate in its predictions. You can use it to predict your mile time from your 3k time, but not your marathon time from your 3k time. Also, if the world record in a particular event was set while the runner was using performance-enhancing drugs, it will predict a faster-than-warranted finishing time in that event, and will similarly give you a lower-than-warranted performance index.*
Outside resources for predicting race times based on previous race times:
- Team Oregon has a chart of equivalent performances, and a pace wizard that you can use with your own times.
- The very detailed IAAF scoring tables, indoor (PDF) and outdoor (PDF).
- The Letsrun conversion table.

* I am personally recognizing the following marks as the valid women's world records:
1500m 3:56
Mile o-4:16.71 i-4:20.5
3000m o-8:21.42
10,000m 29:53.80
These times are not recognized as world records by the IAAF because someone on performance-enhancing drugs ran faster.

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