Ran a 5K? See what you could do in a half or full marathon.
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Riegel's formula predicts a time over a new distance from a known race: T2 = T1 × (D2 ÷ D1)^1.06. The exponent accounts for slowing down over longer distances.
Predictions are most reliable between similar distances and assume you have trained for the longer race; many runners are slower than predicted in their first marathon.
| Race you ran | 5K |
| Other distance | 0 km |
| Your time | 25:00 |
| Fatigue factor | 1.06 |
| Predicted marathon | 3:59:47 |
| Predicted half marathon | 1:55:00 |
| Your pace | 5:00 /km · 8:03 /mi |
Marathon 3:59:47.
| Race you ran | Half marathon |
| Other distance | 0 km |
| Your time | 1:45:00 |
| Fatigue factor | 1.06 |
| Predicted marathon | 3:38:55 |
| Predicted half marathon | 1:45:00 |
| Your pace | 4:59 /km · 8:01 /mi |
Marathon 3:38:55.
About 3:59:47 with Riegel's formula.
Usually within a few minutes for 10K and half-marathon predictions; less for the marathon.
Under 25 minutes is good for most recreational runners; under 20 is very good.
Run the first half at or slightly slower than goal pace, then hold it.