5K to Half Marathon Conversion Calculator
Your 5K time is a strong predictor of Half Marathon performance. This calculator converts your track fitness to a road racing target by factoring in the increased endurance, pacing discipline, and aerobic at 83-88% VO2max required at Half Marathon distance.
Quick answer: a 20:00 5K converts to about 1:37:16 for the half marathon (typical range 1:32:22 to 1:44:18).
5K to Half Marathon conversion table
Estimates only – individual results vary with training, conditions and event experience.
| 5K time | Predicted Half Marathon | Range |
|---|---|---|
| 14:00 | 1:08:05 | 1:04:39–1:13:01 |
| 14:45 | 1:11:44 | 1:08:07–1:16:55 |
| 15:30 | 1:15:23 | 1:11:35–1:20:50 |
| 16:15 | 1:19:01 | 1:15:03–1:24:45 |
| 17:00 | 1:22:40 | 1:18:31–1:28:39 |
| 17:45 | 1:26:19 | 1:21:59–1:32:34 |
| 18:30 | 1:29:58 | 1:25:26–1:36:29 |
| 19:15 | 1:33:37 | 1:28:54–1:40:23 |
| 20:00 | 1:37:16 | 1:32:22–1:44:18 |
| 20:45 | 1:40:55 | 1:35:50–1:48:13 |
| 21:30 | 1:44:33 | 1:39:18–1:52:07 |
| 22:15 | 1:48:12 | 1:42:46–1:56:02 |
| 23:00 | 1:51:51 | 1:46:13–1:59:57 |
| 23:45 | 1:55:30 | 1:49:41–2:03:51 |
| 24:30 | 1:59:09 | 1:53:09–2:07:46 |
| 25:15 | 2:02:48 | 1:56:37–2:11:41 |
| 26:00 | 2:06:26 | 2:00:05–2:15:35 |
| 26:45 | 2:10:05 | 2:03:32–2:19:30 |
| 27:30 | 2:13:44 | 2:07:00–2:23:25 |
| 28:15 | 2:17:23 | 2:10:28–2:27:19 |
| 29:00 | 2:21:02 | 2:13:56–2:31:14 |
| 29:45 | 2:24:41 | 2:17:24–2:35:09 |
How it works
The 5K→Half Marathon conversion blends Riegel's power-law scaling with VDOT oxygen-cost validation. With a 4x distance jump, the predictor applies additional correction factors for the major physiological shift between these events. Where both distances fall within aerobic range, critical speed modeling adds a third reference point. The result is a predicted time with a confidence range.
Training advice
Use a recent race or time-trial 5K for the best prediction. To reach your Half Marathon target, build long runs and marathon-pace work progressively. Half Marathon demands specific preparation — your 5K fitness provides the foundation, but long runs and marathon-pace work closes the gap.
Frequently asked questions
How accurate is a 5K to Half Marathon prediction?
With a recent all-out 5K time, predictions are typically within 4-8% of actual Half Marathon performance. Accuracy improves when the 5K effort is from the past 6-8 weeks under normal conditions.
What training should I do to reach my predicted Half Marathon time?
Focus on long runs and marathon-pace work. Your 5K fitness provides the speed foundation — building aerobic at 83-88% VO2max capacity through progressive training is the key to hitting the target.
Can I use an old 5K time for this prediction?
Recent times (within 6-8 weeks) give the most reliable predictions. Older results may not reflect your current fitness, especially if your training has changed significantly.