100K Pace for 13 Hours — 7:48 per km (12:33 per mile)
100k pace for 13 hours — the answer is 7:48 per kilometre (12:33 per mile). Hold that pace from the start to the finish of the 100K and you will cross the line in 13 hours. This page shows the exact arithmetic, the splits that keep you on target, what that pace feels like, and how to train for it.
There is exactly one pace that produces this finish time at this distance, because pace is time divided by distance and nothing else. The interesting questions are all around that number: how hard it feels, how evenly you can hold it, and what training makes it yours. The rest of this page answers those.
A 100K is 100 km — a distance that takes most runners most of a day and all of their planning. Pace at 100K is an average over running, hiking, aid stations, and the low patches every runner hits; nobody holds one speed for 100 km.
Work out your own pace
Use the race time predictor to check any target time at this distance — enter your goal and it returns the pace per kilometre and per mile, plus the splits. The general pace calculator does the same for any distance, and converts between pace, speed, and finish time. Pace itself is an exact calculation, so the tools agree with the figures on this page to the second.
The formula, shown and cited
Pace per kilometre = finish time ÷ distance (km)
Pace per mile = finish time ÷ distance (miles)
The distance used here is the official standard: the 100K is 100 km (62.14 miles), following the World Athletics standard distances — the marathon is 42.195 km and the half marathon 21.0975 km, and the shorter track distances are exact metric distances. One mile is 1.609344 km, which is why the per-mile pace is always slower numerically than the per-kilometre pace.
Working it through for this page:
13:00:00 ÷ 100 km = 468.0 seconds per km = 7:48 per km
13:00:00 ÷ 62.14 miles = 753.2 seconds per mile = 12:33 per mile
Your average speed for the whole effort is 7.69 km/h (4.78 mph). Speed and pace are the same information expressed two ways — runners talk in pace because it maps directly onto splits and watch readings, while speed is what cyclists and the physics use. Neither is an estimate: given the distance and the time, both are exact.
Your splits for 13 hours
Even pacing at 7:48 per km gives these 5 km splits (with the final partial split at the finish):
| Distance | Cumulative time |
|---|---|
| 5 km | 39:00 |
| 10 km | 1:18:00 |
| 15 km | 1:57:00 |
| 20 km | 2:36:00 |
| 25 km | 3:15:00 |
| 30 km | 3:54:00 |
| 35 km | 4:33:00 |
| 40 km | 5:12:00 |
| 45 km | 5:51:00 |
| 50 km | 6:30:00 |
| 55 km | 7:09:00 |
| 60 km | 7:48:00 |
| 65 km | 8:27:00 |
| 70 km | 9:06:00 |
| 75 km | 9:45:00 |
| 80 km | 10:24:00 |
| 85 km | 11:03:00 |
| 90 km | 11:42:00 |
| 95 km | 12:21:00 |
| 100 km | 13:00:00 |
Splits are the practical half of pacing. A watch showing 7:48 per kilometre tells you nothing unless you know the cumulative time you should see at each marker, and the table above is that checklist. The classic error at every distance is starting 10 to 15 seconds per kilometre too fast in the first quarter and paying for it twice over in the second half — even pacing, or a very slight negative split (second half a touch faster than the first), is the fastest way to hit a target time for almost every runner.
Start at a pace that feels almost embarrassingly easy, walk every climb from the first hour, and treat the first half as a warm-up for the second. Eat from 45 minutes onwards, 60 to 90 g of carbohydrate per hour, and stop properly at aid stations — a two-minute stop to eat and sort your feet saves twenty minutes of shuffling later. Expect at least one low patch and probably a dark patch after sunset; the plan for both is the same: eat, walk a kilometre, and let it pass.
What 7:48 per km means
This is a strong ultra pace — it takes regular training and a solid aerobic base to hold it for the full distance. In training terms, your easy running should sit around 9:03 per km (roughly 60 to 90 seconds per km slower than this target), your tempo running around 8:08 per km, and your interval work faster than target pace in short repetitions with full recoveries. Those three gears are the whole of a training week: easy volume builds the aerobic base, tempo work lifts the speed you can sustain, and intervals lift the ceiling.
| Training zone | Pace per km | Pace per mile |
|---|---|---|
| Easy | 9:03 | 14:34 |
| Steady | 8:33 | 13:46 |
| Tempo | 8:08 | 13:05 |
| Interval | 7:33 | 12:09 |
As a cross-check, the Riegel formula (Riegel, 1981: predicted time = known time × (new distance ÷ known distance)^1.06) translates this performance to other distances, assuming equal fitness and similar conditions: about 32:35 for 5K, 1:07:56 for 10K, 2:29:54 for a half marathon, and 5:12:31 for a marathon. Treat those as estimates, not promises — Riegel is least reliable when the jump in distance is large, and it says nothing about whether you have done the long runs this distance actually requires.
| Distance | Riegel prediction |
|---|---|
| 5K | 32:35 |
| 10K | 1:07:56 |
| half marathon | 2:29:54 |
| marathon | 5:12:31 |
How to train for this target
Train for a day that starts before dawn and ends after dark. The key block is back-to-back long runs: 4 to 5 hours on Saturday and 2 to 3 hours on Sunday, once or twice a month, mostly at easy pace with walking built in on climbs. Practise the whole system — pack, head torch, poles if you use them, shoes, food at 60 to 90 g of carbohydrate per hour, salt, and a crew or drop-bag plan for the halfway point. One midweek tempo session of 20 minutes at tempo pace and two easy runs of 30 to 45 minutes fill the week, with one full rest day. Strength work twice a week, especially calves, quads, and core, protects the downhills. Rehearse a low patch in training: run the last hour of a long run tired and hungry, and practise eating anyway.
On race day, eat a familiar breakfast two to three hours beforehand, sip water rather than gulping it, and start at 7:48 per km from the first step. For efforts over 75 minutes, practise taking on carbohydrate during the long runs — roughly 30 to 60 g per hour — because the gut needs training just like the legs. And remember the safety frame for everything on this site: training targets are estimates, not medical advice, and daily intakes below 1,200 kcal (women) or 1,500 kcal (men) need medical supervision.
What the pace does NOT tell you
Pace is an average, not a speed you hold. The same average pace on a flat road race and a mountain 100K are entirely different efforts: climbs, descents, altitude, and mud all change what any given kilometre costs. A GPS watch reads long on twisty trails — often 3 to 5% — so watch pace is a poor guide on race day; run by effort and by the aid-station splits instead. And the Riegel equivalents above assume road racing at equal fitness; they say nothing about trails, vert, or whether you have done the back-to-back long runs this distance requires.
Pace also says nothing about how you got there. Two runners can hold 7:48 per km with very different heart rates, cadences, and fuel needs, and the Riegel equivalents above assume equal fitness across distances — a sprinter's 5K does not predict their marathon, and a marathoner's 800 m is a poor guide to their 5K. Finally, a target time is a goal, not a verdict: missing it by a minute after a well-run race is a training signal, not a failure, and the right response is to look at the splits, find where it slipped, and adjust the next block.
Related pages
- Pace hub
- 100K Pace for 12 Hours — 7:12 per km (11:35 per mile)
- 100K Pace for 11 Hours — 6:36 per km (10:37 per mile)
Frequently asked questions
What pace do I need for the 100K in 13 hours?
7:48 per kilometre, which is 12:33 per mile. That is the exact figure: 13:00:00 divided by 100 km. Hold it evenly and you finish in 13 hours; the splits table above shows the cumulative time to expect at each marker.
Is 7:48 per km fast?
It is a strong ultra pace. For context, easy running for a runner targeting this time would be around 9:03 per km, and tempo running around 8:08 per km. Whether it feels fast depends on your current fitness — compare it with your recent race paces rather than with anyone else's.
What should my 5K time be if I can run the 100K in 13 hours?
The Riegel formula predicts about 32:35 for 5K from this performance, and about 1:07:56 for 10K. Those are estimates assuming equal fitness and similar conditions; the further the distance from your known result, the less reliable the prediction.
How do I pace the 100K so I hit 13 hours?
Run even splits at 7:48 per km, using the cumulative times in the table above at each marker. Do not start faster — the first kilometre should feel almost too easy. If you are a few seconds slow at halfway, correct by a few seconds per kilometre, not with a sudden surge.
What training do I need to run 7:48 per km for the 100K?
A week with one long run, one tempo or interval session, easy runs between, and one rest day, built over 8 to 12 weeks with volume rising by about 10% a week. Include 20 to 30 minutes at target pace inside the long run in the final weeks, and taper in the last week.
Should I walk during a 100K in 13 hours?
Yes — planned walking is part of the pace, not a failure of it. Walk every climb from the first hour, walk through aid stations, and run the flats and gentle downhills. Holding 7:48 per km on average for 100 km is a run-walk achievement, and the runners who finish are the ones who walked early and still had legs for the last 30 km.
Estimates only, not medical advice. Minimum safe intakes: 1,200 kcal/day women, 1,500 kcal/day men — consult a healthcare professional before a very-low-calorie diet.