Half Marathon Pace Calculator
Enter a target half marathon finish time to see the average pace per kilometre and per mile you would need to hold, plus an even-effort split table across the 13.1-mile race.
Required pace per km
04:59 / km
- Pace per km
- 04:59 / km
- Pace per mile
- 08:01 / mi
- Speed
- 12.06 km/h
- Speed (mph)
- 7.49 mph
- Split — 5K (5.00 km)
- 24:53
- Split — 10K (10.00 km)
- 49:46
- Split — Halfway (10.55 km)
- 52:30
- Split — 15K (15.00 km)
- 1:14:39
- Split — 10 miles (16.09 km)
- 1:20:06
- Split — 20K (20.00 km)
- 1:39:32
- Split — Finish (21.10 km)
- 1:45:00
Required pace = target finish time ÷ 21.0975 km (the half marathon distance — exactly half the World Athletics marathon of 42.195 km, TR4.3). Splits assume even effort — each is the elapsed clock time you should hit at that distance. Real races usually run slight positive splits; treat the back-half splits as a target, not a guarantee. Mile ↔ km uses the NIST exact factor 1 mile = 1.609344 km.
How to use this calculator
Enter your goal half marathon finish time in hours, minutes and seconds — 2:00:00 is the classic mass-participation benchmark, 1:45:00 is a strong club-runner target, and 1:30:00 is the "sub-90" line many experienced amateurs chase. Pick whether you want the headline pace shown per kilometre or per mile. The breakdown lists pace per km, pace per mile, average speed in km/h and mph, and an even-effort split table showing the clock time you should hit at 5K, 10K, the halfway point (10.54875 km), 15K, 10 miles (16.09344 km), 20K, and the finish (21.0975 km). Use the splits to set watch alerts or to check whether you are on pace at each marker.
How the calculation works
The maths is one identity: required pace equals target time divided by distance. The half marathon distance is 21.0975 km — exactly half the marathon distance of 42.195 km fixed by World Athletics in Technical Rule TR4.3 "Distances of Road Races". Mile-to-kilometre conversion uses the NIST exact factor of 1 international mile = 1.609344 km (NIST SP 811:2008, Appendix B.8), which makes the half marathon 13.10938 miles — the familiar "13.1". Speed in km/h is 21.0975 ÷ (target_seconds / 3600); mph multiplies by 0.6213712 exactly. Splits are the constant pace multiplied by each split distance, so they describe even-effort pacing. In practice most runners record small positive splits (the second half slower than the first) because of glycogen depletion and heat build-up, so the back-half splits here are a target rather than a prediction. Because a half marathon required pace equals twice-the-distance-halved, the per-km pace for any half marathon time is identical to the per-km pace of the marathon run in exactly double that time: a 1:45:00 half and a 3:30:00 marathon share the same 4:59 per km.
Worked example
Target: a sub-1:45 half marathon, 1:45:00 = 6,300 seconds. Required pace per km = 6,300 ÷ 21.0975 = 298.61 s/km, which rounds to 4:59 per km. Per mile: 6,300 ÷ 13.10938 = 480.57 s/mile, which rounds to 8:01 per mile. Average speed: 21.0975 km ÷ 1.75 h = 12.06 km/h, or 7.49 mph. Even-effort splits at 4:59 per km: 5K at 24:53, 10K at 49:46, halfway at 52:30 flat, 15K at 1:14:39, 10 miles at 1:20:06, 20K at 1:39:32, finish at 1:45:00. If you know you tend to fade, bank 10-20 seconds over the first 5K rather than the whole cushion up front — the energetic cost of going out too hard grows nonlinearly with pace.
Frequently asked questions
How do I work out the pace I need for a half marathon time?
Divide the target time in seconds by the half marathon distance. The half marathon is 21.0975 km (half of the World Athletics marathon of 42.195 km) or 13.10938 miles. For a 2:00:00 half: 7,200 seconds ÷ 21.0975 km = 341.27 s/km, which is 5 minutes 41 seconds per km, or 9 minutes 9 seconds per mile. For 1:45:00: 6,300 ÷ 21.0975 = 298.61 s/km = 4:59 per km = 8:01 per mile. For 1:30:00: 5,400 ÷ 21.0975 = 255.96 s/km = 4:16 per km = 6:52 per mile.
What pace is a sub-2 hour half marathon?
5:41 per km or 9:09 per mile, held for the full 13.1 miles. Sub-2:00 is the single most popular half marathon goal — it is roughly the median finish for trained recreational runners and the threshold where most organised pacing groups start. To carry a small cushion, aim for about 5:38 per km (a 1:58:45 projection) so a slight fade in the final 5K still lands you under two hours.
What is a good half marathon time?
It depends on age, sex and training, but useful reference points for recreational runners are: finishing (any time) for a first-timer, sub-2:00:00 for a committed amateur, sub-1:45:00 for a strong club runner, and sub-1:30:00 for an experienced competitive amateur. Elite men run under 60 minutes and elite women under 65 minutes. The world records (Jacob Kiplimo 56:42, 2024; Letesenbet Gidey 1:02:52, 2021) equate to roughly 2:41 and 2:59 per km respectively.
Should I run even splits or negative splits in a half marathon?
Negative splits — a slightly faster second half — are associated with better outcomes in race data, but the half marathon is short enough that a well-judged even effort works well for most runners. The common mistake is a fast first 5K driven by adrenaline and a crowded start. A practical plan is to run the first 5K about 5-10 seconds per km slower than goal pace, settle into goal pace through 15K, then push the final 6K if you have the legs. The even-effort splits in this calculator are the reference line to check yourself against at each marker.
How does half marathon pace relate to marathon pace?
For the same required per-km pace, a marathon takes exactly twice the time of a half marathon, because the marathon is exactly twice the distance. So a 1:45:00 half and a 3:30:00 marathon are both run at 4:59 per km. In practice, though, nobody sustains their half marathon pace for a full marathon — a widely used rule of thumb is that your marathon pace is roughly 8-10 % slower per km than your half marathon pace, reflecting the extra fatigue of the longer distance.
How do I convert pace per kilometre to pace per mile?
Multiply by 1.609344 (the NIST exact conversion factor). A 5:00 per km pace is 5 × 1.609344 = 8.047 minutes per mile, or 8 minutes 2.8 seconds per mile. Going the other way, divide by 1.609344: 8:00 per mile is 8 ÷ 1.609344 = 4.971 minutes per km, or 4 minutes 58.3 seconds per km. Rule of thumb: pace per mile is about 60 % bigger than pace per km because a mile is about 60 % longer than a kilometre.