5K to Half Marathon Race Equivalency
Your 5K time is a reliable measure of aerobic capacity. This table shows what that capacity predicts for the half marathon — assuming threshold-specific training and half marathon-appropriate long runs. The physiological distance is bridgeable with the right training additions.
Quick answer: A 22:00 5K runner (RPI 44.5) has equivalent Half Marathon fitness of 1:41:11 (7:43/mi). Range in this table: 16:00 5K → 1:13:18 Half Marathon through 35:00 → 2:40:47.
5K → Half Marathon Equivalency Table
| 5K Time | RPI | Half Marathon Equivalent | Equiv Pace |
|---|---|---|---|
| 16:00 | 64.6 | 1:13:18 | 5:35/mi(3:28/km) |
| 17:00 | 60.2 | 1:17:55 | 5:57/mi(3:42/km) |
| 18:00 | 56.3 | 1:22:34 | 6:18/mi(3:55/km) |
| 19:00 | 52.9 | 1:27:10 | 6:39/mi(4:08/km) |
| 20:00 | 49.8 | 1:31:50 | 7:00/mi(4:21/km) |
| 21:00 | 47 | 1:36:32 | 7:22/mi(4:35/km) |
| 22:00 | 44.5 | 1:41:11 | 7:43/mi(4:48/km) |
| 24:00 | 40.2 | 1:50:26 | 8:25/mi(5:14/km) |
| 26:00 | 36.6 | 1:59:35 | 9:07/mi(5:40/km) |
| 28:00 | 33.5 | 2:08:53 | 9:50/mi(6:07/km) |
| 30:00 | 30.8 | 2:18:17 | 10:33/mi(6:33/km) |
| 35:00 | 25.6 | 2:40:47 | 12:16/mi(7:37/km) |
Computed via Daniels/Gilbert oxygen cost equation (1979). Predictions assume distance-specific training is in place.
How accurate is this prediction?
The 5K → half marathon prediction is accurate when half marathon-specific training is in place: long runs of 12–15 miles and threshold tempo runs (25–35 minutes). Without these, most 5K-trained runners underperform their half marathon equivalent by 5–10 minutes. With them, the typical gap closes to 2–4 minutes.
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
What training converts 5K fitness to half marathon fitness?
Add two key elements to 5K training: weekly threshold tempo runs (25–35 minutes at threshold pace) and long runs building to 12–15 miles at easy pace. These develop the sustained effort and aerobic endurance that 5K training alone does not.
What half marathon does a 20:00 5K predict?
A 20:00 5K (RPI 49.8) projects to 1:31:50 half marathon fitness at 7:00/mi. This assumes half-marathon specific preparation is in place.
Is the 5K to half marathon equivalency reliable?
Reliable when half-specific training exists. The 5K measures aerobic capacity that the half marathon uses — but the half demands sustained effort for 70–120 minutes, which requires specific endurance development beyond what 5K training produces.