How to use the pace calculator
- Pick your mode. Choose I know my goal time to get the pace you need, or I know my pace to see your finishing time.
- Choose a distance. 5K, 10K, half marathon (21.0975 km), marathon (42.195 km) or a custom distance.
- Read the result. You get pace per km and per mile, average speed, finish times for other distances at the same pace, and a full table of kilometre splits.
Everything updates as you type. Nothing is sent anywhere: the calculator runs entirely in your browser.
Common half marathon goal paces
| Goal time | Pace per km | Pace per mile |
|---|---|---|
| 1:30:00 | 4:16 | 6:52 |
| 1:45:00 | 4:59 | 8:01 |
| 1:50:00 | 5:13 | 8:23 |
| 2:00:00 | 5:41 | 9:09 |
| 2:15:00 | 6:24 | 10:18 |
| 2:30:00 | 7:07 | 11:27 |
Check your goal against the race’s time limit before you enter. Many Spanish half marathons close the course at 2 h 30 min, and a few are stricter (2 h 15–2 h 20).
Why pace matters in training
Race pace is only one of the paces in a good training plan:
- Easy runs should feel conversational, usually 60–90 seconds per km slower than half marathon pace. They build your aerobic base and help you recover.
- Tempo or threshold runs sit close to the pace you could hold for about an hour. They raise your lactate threshold, the point where fatigue builds quickly.
- Intervals (for example 800 m or 1 km repeats) are faster than race pace and develop VO2 max and running economy.
- Long runs are mostly easy, sometimes with blocks at goal race pace late in the run.
Running every session at the same “medium” pace is one of the most common reasons runners stop improving. Use the calculator to set a pace for each type of session, then check it against your heart rate or perceived effort.
Pacing on race day
- Start controlled. The first 3 km of a half marathon should feel easy. Going 10 seconds per km too fast early costs far more time later than it gains.
- Aim for even or slightly negative splits. Print or memorise your 5 km checkpoints from the splits table.
- Adjust for the course. Hilly races (Segovia, Álora, Palas de Rei) and hot or windy days call for pacing by effort rather than by the watch.
- Use the pacers. Many Spanish races run pace groups from about 1:20 to 2:00. Check the race page in our calendar.
Frequently asked questions
How is pace calculated? Pace = total time ÷ distance. A 2:00:00 half marathon is 7,200 seconds ÷ 21.0975 km = 341 seconds, or 5:41 per km.
Why does my GPS watch show a longer distance than 21.1 km? Certified courses are measured on the shortest possible line. Weaving around other runners and GPS error usually add 100–300 m, so aim a few seconds per km faster than your calculated pace.
Can this predict my marathon time from a half? The same pace, other distances list shows times at an identical pace. Real marathon times are usually slower. A common rule of thumb is to double your half marathon time and add 5–10%.