Testing the Converters

What sort of time might you expect to run a marathon based on your performance at shorter distances? It's a common question, for first-timers especially. There are plenty of conversion calculators on the Web; my favorite is this one. But recently I've heard about some simple equations, one that you can crunch in your head and two that you can do easily with a pencil and paper. Let's try 'em out.

There's the one that says your marathon time will be twice your half-marathon time plus 10 minutes. For me, that's 1:28:51 x 2 = 2:57:42. Then add 10 and you get 3:07:42. That's less than 90 seconds more than my actual marathon PR. Not bad.

Hal Higdon's formula is your 10K time multiplied by 4.66. So we've got 39:13 x 4.66 = 3:02:45. A little quick there, about three and a half minutes too fast, but still not bad.

Last one says simply add 20 seconds per mile for each doubling of your distance. My best half-marathon pace is 6:47 (actually, 6:46.7). Add 20 to that to get 7:06.7 x 26.2 = 3:06:35. Wow—that's almost spot-on, a mere 19 seconds slower than my PR.

Of course, the old caveat that goes with any conversion to a marathon time still applies: If you haven't been doing the kind of long runs that are key to adapting your body to run 26.2 — as opposed to run 18, shuffle four, walk four more and then crawl the final 0.2 — these are all meaningless.