Marathon Pace Calculator
Enter a target marathon finish time to see the average pace per kilometre and per mile you would need to hit, plus an even-effort split table at every 5K and the half-marathon mark.
Required pace per km
05:41 / km
- Pace per km
- 05:41 / km
- Pace per mile
- 09:09 / mi
- Speed
- 10.55 km/h
- Speed (mph)
- 6.55 mph
- Split — 5K (5 km)
- 28:26
- Split — 10K (10 km)
- 56:53
- Split — 15K (15 km)
- 1:25:19
- Split — 20K (20 km)
- 1:53:45
- Split — Half marathon (21.0975 km)
- 2:00:00
- Split — 25K (25 km)
- 2:22:12
- Split — 30K (30 km)
- 2:50:38
- Split — 35K (35 km)
- 3:19:05
- Split — 40K (40 km)
- 3:47:31
- Split — Finish (42.195 km)
- 4:00:00
Required pace = target finish time ÷ 42.195 km (the World Athletics marathon distance, TR4.3). Splits assume even effort — each is the elapsed clock time you should hit at that distance. Real marathons usually run 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 marathon finish time in hours, minutes and seconds — 4:00:00 is the classic "sub-4" benchmark, 3:30:00 is a Boston-qualifier ballpark for many age groups, and 2:59:59 is the elite "sub-3" line. 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 every 5K marker (5K, 10K, 15K, 20K, 25K, 30K, 35K, 40K), the half marathon (21.0975 km), and the finish (42.195 km). Use the splits to set your watch alerts or to brief the crew at your aid stations.
How the calculation works
The maths is one identity: required pace equals target time divided by distance. The marathon distance is fixed at 42.195 km by World Athletics in Technical Rule TR4.3 "Distances of Road Races", and the half marathon at exactly half that, 21.0975 km. Mile-to-kilometre conversion uses the NIST exact factor of 1 international mile = 1.609344 km (NIST SP 811:2008, Appendix B.8). Speed in km/h is 42.195 ÷ (target_seconds / 3600); mph multiplies by 0.6213712 exactly. Splits are the constant pace multiplied by each split distance — they describe even-effort pacing. In a real marathon you usually run positive splits (the back half is slower than the front half) because of glycogen depletion, dehydration and heat build-up, so the back-half splits here are a target rather than a prediction. The marathon distance itself dates to the 1908 London Olympics, where the course ran 26 miles from Windsor Castle to the White City stadium plus 385 yards to finish in front of King Edward VII's royal box, totalling 42.195 km, and was codified internationally by the IAAF in 1921.
Worked example
Target: sub-4 marathon, 4:00:00 = 14,400 seconds. Required pace per km = 14,400 ÷ 42.195 = 341.27 s/km, which rounds to 5:41 per km. Per mile: 14,400 ÷ 26.21876 = 549.22 s/mile, which rounds to 9:09 per mile. Average speed: 42.195 km ÷ 4 h = 10.55 km/h, or 6.55 mph. Even-effort splits at 5:41 per km: 5K at 28:25, 10K at 56:51, 15K at 1:25:16, half marathon at 2:00:00 flat, 20K at 1:53:42, 25K at 2:22:08, 30K at 2:50:33, 35K at 3:18:59, 40K at 3:47:24, finish at 4:00:00. Bank a few seconds in the first half if you know you tend to fade — but no more than 30-60 seconds total, since the energetic cost of running too fast early grows nonlinearly with pace.
Frequently asked questions
How do I work out the pace I need for a marathon time?
Divide the target time in seconds by the marathon distance. The marathon is 42.195 km (World Athletics TR4.3) or 26.21876 miles. For a 4:00:00 marathon: 14,400 seconds ÷ 42.195 km = 341.27 s/km, which is 5 minutes 41 seconds per km, or 9 minutes 9 seconds per mile. For 3:30:00: 12,600 ÷ 42.195 = 298.61 s/km = 4:59 per km = 8:01 per mile. For 3:00:00: 10,800 ÷ 42.195 = 256.0 s/km = 4:16 per km = 6:52 per mile.
What pace is a sub-4 marathon?
5:41 per km or 9:09 per mile, held constantly for 26.2 miles. The "sub-4" line is symbolic in recreational marathoning — roughly the median for trained club runners and the threshold where most pacing groups start. To bank a small cushion, aim for 5:38 per km (3:57:30 projected) so a small fade in the last 10K still lands you under 4 hours.
What pace is a Boston-qualifier marathon time?
The Boston Athletic Association sets Boston Marathon qualifying times by age and sex. For men 18-34 the standard is 3:00:00 (4:16 per km, 6:52 per mile); for women 18-34 it is 3:30:00 (4:59 per km, 8:01 per mile). Standards loosen with age. The B.A.A. also requires that runners exceed the standard by a margin (which has been growing) because the field is oversubscribed; check baa.org for the current cut-off.
Should I aim for even splits or negative splits?
Negative splits — running the second half faster than the first — are statistically associated with faster overall finish times in marathon data sets. The mechanism is simple: starting at a sustainable pace conserves glycogen for the second half, where most runners hit the wall around 30-35 km if they have overspent the energy budget. The even-effort splits in this calculator are a useful reference, but pacing strategy literature (e.g. Renato Canova) generally recommends running the first 5-10 km 5-15 seconds per km slower than goal pace, then settling into goal pace until 30 km, then attacking if you have the legs.
How accurate are even-pace marathon splits in practice?
Even splits are mathematically clean but rare in practice. A study of 9,789 finishers at the 2008 Berlin Marathon (Diaz et al., 2017) found mean positive splits of 7-9 % — the second half was 7-9 % slower than the first. Recreational marathoners average closer to 12-15 % positive splits. Use the even-effort splits here as a sanity check ("am I on pace at 20K?") rather than as a strict race plan. If your 20K split is 10 % faster than the even-effort target, you are almost certainly going out too hard.
Why is the marathon 42.195 km exactly?
The distance was fixed at the 1908 London Olympics: the course ran 26 miles from Windsor Castle to the finish at the White City stadium, then 385 yards inside the stadium so the finish line was in front of the royal box of King Edward VII. 26 miles 385 yards = 42,195 m = 42.195 km. The IAAF (now World Athletics) adopted this as the official marathon distance in 1921 and it has not changed since — every Olympic, World Championship, World Marathon Majors and certified course race runs the same 42.195 km.
How do I convert pace per kilometre to pace per mile?
Multiply by 1.609344 (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.