How recent should the input race be?

Ideally within the last 6-8 weeks, run all-out on a course similar to your target race.

Does it work for trail running?

No: elevation and terrain change the effort too much. The formula is meant for flat road races.

Race time predictor (5K, 10K, half, marathon)

Enter the distance and time of a recent all-out race or test. The calculator estimates what you could run over the other classic distances.

Reference race distance (km)Finish time (h:mm:ss)

23:59 (4:48 min/km)

10K

50:00 (5:00 min/km)

Half marathon

1:50:19 (5:14 min/km)

Marathon

3:50:01 (5:27 min/km)

Embed on your site or blog

Free for blogs, clubs and sports teams: copy the code and paste it into your page.

<iframe src="https://www.velunite.it/embed/strumenti/marathon-race-time-predictor" width="100%" height="480" style="border:0;border-radius:16px;max-width:720px" loading="lazy" title="Race time predictor (5K, 10K, half, marathon) — Velunite"></iframe>
<p style="font-size:13px"><a href="https://www.velunite.it/en/strumenti/marathon-race-time-predictor">Race time predictor (5K, 10K, half, marathon) — Velunite</a></p>

How the prediction works

We use Riegel's formula: T2 = T1 × (D2 / D1)^1.06. The 1.06 exponent accounts for the fact that the longer the race, the slower the pace you can sustain.

Example: a 50-minute 10K predicts about 1:50 for the half marathon and 3:50 for the marathon.

When the prediction is wrong

For the marathon the estimate is optimistic if you have not done 28-32 km long runs: without volume, the wall at 30 km slows down even fast 10K runners.

The estimate is more reliable when the input race is close to the target distance: to predict a marathon, use a half, not a 5K.

FAQ

How recent should the input race be?: Ideally within the last 6-8 weeks, run all-out on a course similar to your target race.
Does it work for trail running?: No: elevation and terrain change the effort too much. The formula is meant for flat road races.