10K to Half Marathon Race Equivalency
The 10K and half marathon are the most physiologically similar standard race distances — both demand sustained effort near the lactate threshold for 30–90 minutes. This makes the 10K → half marathon equivalency the most reliable cross-distance prediction available. The table below shows predicted half marathon times for a range of 10K inputs, all computed from the Daniels/Gilbert oxygen cost equation.
Quick answer: A 48:00 10K runner (RPI 42) has equivalent Half Marathon fitness of 1:46:22 (8:07/mi). Range in this table: 32:00 10K → 1:10:33 Half Marathon through 70:00 → 2:35:01.
10K → Half Marathon Equivalency Table
| 10K Time | RPI | Half Marathon Equivalent | Equiv Pace |
|---|---|---|---|
| 32:00 | 67.5 | 1:10:33 | 5:23/mi(3:21/km) |
| 35:00 | 60.7 | 1:17:21 | 5:54/mi(3:40/km) |
| 38:00 | 55.2 | 1:24:01 | 6:25/mi(3:59/km) |
| 40:00 | 51.9 | 1:28:37 | 6:46/mi(4:12/km) |
| 42:00 | 49.1 | 1:32:58 | 7:05/mi(4:24/km) |
| 45:00 | 45.3 | 1:39:40 | 7:36/mi(4:43/km) |
| 48:00 | 42 | 1:46:22 | 8:07/mi(5:03/km) |
| 50:00 | 40 | 1:50:53 | 8:27/mi(5:15/km) |
| 55:00 | 35.8 | 2:01:53 | 9:18/mi(5:47/km) |
| 60:00 | 32.3 | 2:12:54 | 10:08/mi(6:18/km) |
| 65:00 | 29.3 | 2:24:03 | 10:59/mi(6:49/km) |
| 70:00 | 26.8 | 2:35:01 | 11:49/mi(7:21/km) |
Computed via Daniels/Gilbert oxygen cost equation (1979). Predictions assume distance-specific training is in place.
How accurate is this prediction?
The 10K → half marathon prediction is the most accurate in the equivalency system. Both distances tax the same aerobic and threshold energy systems. Runners with consistent weekly training at both distances typically match their equivalency within two to four minutes. The main divergence factor: half marathon-specific long runs (12–15 miles) develop pacing stamina that shorter training blocks do not.
Equivalency predicts potential — training determines actuals
This table shows what your aerobic capacity predicts at a different distance. StrideIQ tracks whether your training is actually developing the distance-specific fitness needed to meet that potential — long-run adaptation, pacing control, threshold stamina — from your own workout data.
Common questions
How accurate is the 10K to half marathon equivalency?
Very accurate — this is the most reliable cross-distance pair in running equivalency. The 10K and half marathon both require sustained effort near lactate threshold, so the aerobic capacity measured by the 10K closely predicts half marathon performance. Most consistently trained runners fall within three to five minutes of their prediction. The gap widens for runners who have done much more 10K-specific training than half marathon preparation.
What half marathon time does a 45:00 10K predict?
A 45:00 10K gives an RPI of 45.3. The equivalent half marathon is 1:39:40 at 7:36/mi. This assumes comparable half marathon preparation. If you have only raced 10Ks and not half marathons, add 3–5 minutes for unfamiliarity with the longer distance until you have race-specific experience.
If I can run 40:00 for 10K, what half marathon time is realistic?
A 40:00 10K runner (RPI 51.9) has the aerobic capacity for a 1:28:37 half marathon. Half marathon race pace (6:46/mi) runs about 10–15 seconds per mile slower than 10K race pace — which is exactly what the lactate threshold demands of running 13.1 miles versus 6.2 miles. Train at threshold pace and your half marathon time will naturally drop toward its equivalent.