A marathon or half in. Your ultra out.
Type a recent marathon or half time. We project your 50K finish using the Riegel formula. Caveat: ultra terrain and elevation can add 5-15% to predictions.
From 10K in 50:00, here are your projected race times.
Find Marathon races →Reference table — popular race times and the Riegel-projected 50K. Real ultra finishes tend to be slower due to terrain, elevation, and fueling demands.
| Input race result | Predicted | Notes |
|---|---|---|
| Marathon 3:00:00 | 50K ~3:38 | Elite ultra territory. |
| Marathon 3:30:00 | 50K ~4:13 | Strong amateur ultra. |
| Marathon 4:00:00 | 50K ~4:48 | Solid first-50K target. |
| Marathon 4:30:00 | 50K ~5:23 | Comfortable 50K finish. |
| Half 1:45:00 | 50K ~4:23 | From half is risky — half is < ½ of 50K. |