A 5K takes as long as your pace times five kilometers. At 6:00 per kilometer that is exactly 30:00. At 5:00/km it is 25:00. At 8:00/km it is 40:00. There is no separate “average 5K” hiding behind the multiplication.
The distance is 5.000 km, which is 3.107 miles, not 3 miles and not 5 miles.
5K pace chart
| Pace /km | Pace /mile | 5K time | Speed |
|---|---|---|---|
| 4:00 | 6:26 | 20:00 | 15.0 km/h |
| 4:30 | 7:15 | 22:30 | 13.3 km/h |
| 5:00 | 8:03 | 25:00 | 12.0 km/h |
| 5:30 | 8:51 | 27:30 | 10.9 km/h |
| 6:00 | 9:39 | 30:00 | 10.0 km/h |
| 7:00 | 11:16 | 35:00 | 8.6 km/h |
| 8:00 | 12:52 | 40:00 | 7.5 km/h |
| 12:00 /mile | 7:27 /km | 37:17 | 8.0 km/h |
The last row starts from a mile pace, which is how many US plans are written. Twelve minutes per mile is not twelve minutes per kilometer. The 5K pace calculator accepts either unit and prints a split for each kilometer.
Three miles is a shorter race
Three miles is 4.828 km. At 6:00/km that is about 28:58, roughly a minute faster than a 30:00 5K. If a result says “3 mile” and you compare it with a parkrun, convert the distance before you compare the clocks. The pace calculator takes a custom distance for that.
What the second half does
Even splits are the planning table. A first 5K often goes out faster than the average and comes back slower. If kilometer 1 is 5:20 and the goal is 6:00 average, the remaining four kilometers have to average 6:10 to finish in 30:00. The split calculator shows the even version so you can see the damage.
A 5K time also projects other races, with a slowdown built in. The race time predictor does that. Doubling a 5K to estimate a 10K is the version that assumes you do not slow down at all. How long a 10K takes is the direct table if you already know the 10K pace.