Half Marathon Pace Calculator (13.1 Miles)

A half marathon is 13.1094 miles, or 21.0975 km — exactly half of the marathon and not a round number in either unit. Enter your goal finish time to see the pace it demands. The distance is already loaded.

Worked example: two hours flat

Pace = time ÷ distance = 120:00 ÷ 21.0975 km = 5:41/km, which is 10.55 km/h and 9:09 per mile.

The decimals are not pedantry here. Pace a two-hour half off a round “21 km” and you get 5:43/km, which finishes at 2:00:36 — the fractional 97.5 meters at the end are worth about 33 seconds, more than enough to miss the target you trained for six months to hit.

Goal times and their paces

Goal time	Pace (min/km)	Pace (min/mile)	Speed
1:30	4:16	6:52	14.06 km/h
1:45	4:59	8:01	12.06 km/h
2:00	5:41	9:09	10.55 km/h
2:15	6:24	10:18	9.38 km/h
2:30	7:07	11:27	8.44 km/h
2:45	7:49	12:35	7.67 km/h

Fifteen minutes of finish time costs roughly 43 seconds per kilometer, or 1:09 per mile. That is a coarse dial: there is no such thing as a small pacing mistake over this distance, because every error is multiplied by 13.

Why this distance behaves differently

The half sits at the boundary of what most runners can hold without eating. Under about 90 minutes the race is essentially a long threshold effort; past two hours it starts to look like a marathon in miniature, with fluid, fuel and heat all entering the equation. That is why the same runner can nail a 10K plan and blow up in a half — the failure is rarely aerobic.

World Athletics notes that organizers invented the distance in the 1950s as an alternative to the full marathon, and that many runners now use it as a stepping stone toward one. The stepping-stone framing is worth taking literally: it is the shortest race where marathon habits (fueling early, starting conservatively, drinking on a schedule) can be rehearsed at real intensity.

Pace the race in two halves

The 10.5 km mark is a genuine decision point, and running the second half faster than the first is the strategy with the best evidence behind it — see the negative split calculator for how large the difference should be.

If the half is a checkpoint on the way to the full, the marathon pace calculator shows what the same effort looks like at double the distance, and the 10K pace calculator covers the shorter tune-up races. For any other distance, use the running pace calculator.