What pace is, and why runners use it instead of speed
Pace is elapsed time divided by distance: the number of minutes and seconds it takes you to cover one mile or one kilometre. Speed is the same relationship turned upside down — distance divided by time. Both describe exactly the same run, and this calculator gives you both, because the two worlds you move between use different ones. Your watch and your training plan talk in pace. A treadmill console, a bike computer and a physiology lab talk in speed.
Runners default to pace for a practical reason: it converts to race time by multiplication. If you know you can hold 8:00 per mile, the marathon is 26.2188 × 8:00, and you can do that in your head on the start line. Speed forces a division instead, and division under race stress is how people mis-split.
The reciprocal relationship has a consequence worth internalising. Going from 10:00 to 9:30 per mile — thirty seconds — raises speed from 6.00 to 6.32 mph, a gain of 0.32 mph. Going from 6:00 to 5:30 per mile, the same thirty seconds, raises speed from 10.00 to 10.91 mph, a gain of 0.91 mph. The faster you already are, the more physiological work each second of pace costs. That is why elite marathon improvements come in seconds while a new runner's come in minutes.
The formula, one term at a time
Everything on this page comes from p = t ÷ d. The work is in the units, so handle them explicitly.
Convert the time to a single number first. A finish of 1 hour 45 minutes 30 seconds is 1×3600 + 45×60 + 30 = 6,330 seconds. Working in seconds avoids the mixed-base arithmetic that produces most hand-calculation errors.
Convert the distance to one unit. The calculator works internally in miles, using the international mile of exactly 1,609.344 metres. That definition is exact by agreement, not a rounded approximation, so 1 km = 0.621371192 mi to as many digits as you like.
Divide, then convert back. 6,330 s ÷ 13.1094 mi = 482.9 s/mi = 8:03 per mile. To get minutes per kilometre, multiply the seconds-per-mile figure by 0.621371192: 482.9 × 0.621371192 = 300.1 s/km = 5:00 per kilometre. To get mph, divide 3,600 by the seconds per mile: 3,600 ÷ 482.9 = 7.46 mph.
Note that pace converts between miles and kilometres by multiplying by 0.621371192, while distance converts by dividing. This trips people up constantly. A pace per kilometre is always the smaller number, because a kilometre is the shorter distance and takes less time to cover.
Worked example: a 1:45:00 half marathon
You want to run the half marathon in 1 hour 45 minutes. The half marathon is 21.0975 km, which is 21.0975 ÷ 1.609344 = 13.1094 miles.
- Time to seconds. 1×3600 + 45×60 + 0 = 3,600 + 2,700 = 6,300 s.
- Seconds per mile. 6,300 ÷ 13.1094 = 480.6 s/mi.
- Back to mm:ss. 480.6 s = 8 minutes with 0.6 s left over, so 8:01 per mile.
- Per kilometre. 480.6 × 0.621371192 = 298.6 s = 4:59 per kilometre.
- Speed. 3,600 ÷ 480.6 = 7.49 mph, or 7.49 × 1.609344 = 12.05 km/h.
Now use the same pace forward. At 480.6 s/mi, the 10 km split is 6.2137 × 480.6 = 2,986 s = 49:46, and the marathon at that pace would be 26.2188 × 480.6 = 12,601 s = 3:30:01 — which is exactly double, because pace held constant makes time proportional to distance. Whether you could hold it for twice the distance is a different question, and the race time prediction calculator answers that one.
How to read the result and turn it into a race plan
A single average pace hides the shape of the run, and the shape is what decides whether you finish strong. Three ways to use the number:
As a ceiling, not a target, for the first mile. The most reliable pattern in distance racing is the even or slightly negative split — the second half run at the same pace or a few seconds faster. Starting 15 seconds per mile faster than goal pace feels effortless for two miles and costs far more than 15 seconds per mile over the closing third of a marathon.
Adjusted for the course, not the map. Hills cost more time going up than they return coming down, so an out-and-back with 500 ft of climb runs slower than the same distance flat even though the net elevation change is zero. Set your target pace on effort for the climbs and let the flat sections average out.
Cross-checked against a physiological anchor. If your goal pace sits above your lactate threshold, no amount of discipline will hold it to the finish. Check it against your training zones with the heart rate zones calculator, or against a race-derived fitness score with the VDOT calculator. A marathon goal pace should feel comfortably conversational in the first hour.
Two practical cautions on measurement. GPS watches typically over-report distance on a certified course, because the receiver samples position with error and every wobble adds length — so your watch may show 26.4 miles for a 26.2188-mile race and report a pace faster than the official one. And race courses are certified to the shortest possible route between the timing points, which almost nobody actually runs.
Race finish times by pace per mile
| Pace per mile | Pace per km | 5 km | 10 km | Half marathon | Marathon |
|---|---|---|---|---|---|
| 6:00 | 3:44 | 18:38 | 37:17 | 1:18:39 | 2:37:19 |
| 6:30 | 4:02 | 20:12 | 40:23 | 1:25:13 | 2:50:25 |
| 7:00 | 4:21 | 21:45 | 43:30 | 1:31:46 | 3:03:32 |
| 7:30 | 4:40 | 23:18 | 46:36 | 1:38:19 | 3:16:38 |
| 8:00 | 4:58 | 24:51 | 49:43 | 1:44:53 | 3:29:45 |
| 8:30 | 5:17 | 26:24 | 52:49 | 1:51:26 | 3:42:52 |
| 9:00 | 5:36 | 27:58 | 55:55 | 1:57:59 | 3:55:58 |
| 9:30 | 5:54 | 29:31 | 59:02 | 2:04:32 | 4:09:05 |
| 10:00 | 6:13 | 31:04 | 1:02:08 | 2:11:06 | 4:22:11 |
| 10:30 | 6:31 | 32:37 | 1:05:15 | 2:17:39 | 4:35:18 |
| 11:00 | 6:50 | 34:11 | 1:08:21 | 2:24:12 | 4:48:24 |
| 12:00 | 7:27 | 37:17 | 1:14:34 | 2:37:19 | 5:14:38 |
Generated by running this calculator at each pace. Distances used: 5 km = 3.10686 mi, 10 km = 6.21371 mi, half marathon = 13.10938 mi, marathon = 26.21875 mi.
Mistakes that make a pace number wrong
- Mixing the two conversion directions. Distance in km ÷ 1.609344 gives miles; pace in min/mi × 0.621371 gives min/km. Using the same operation for both is the single most common error, and it produces a plausible-looking number that is wrong by 2.6×.
- Treating a half marathon as 13.1 miles. The half marathon is 21.0975 km = 13.1094 miles. The 0.0094 mile difference is only about 4.5 seconds at 8:00 pace, but the marathon rounding error is twice that, and it is free to avoid.
- Averaging paces instead of averaging times. If you run one mile at 7:00 and one at 9:00, your average pace is 8:00 — because the distances are equal. Run 1 mile at 7:00 and 3 miles at 9:00 and the average is 8:30, not 8:00. Always add the times and divide by the total distance.
- Using watch distance for pace on a certified course. Take the official distance and your official time; a watch that reads long makes your pace look faster than it was.
- Planning a marathon at a pace derived from a 5 km time. Pace is not conserved across distances. Scale it with an endurance model, not by assuming it holds.
- Forgetting that treadmill speed is not road pace. A treadmill belt does the horizontal work for you at 0% grade; most coaches set 1% incline to approximate outdoor effort. The treadmill incline pace calculator handles that conversion.
Even splits are a plan, not a law
Holding one pace for the whole race is the right default on a flat course, and every row of the table above assumes it. On a rolling or point-to-point course, plan by effort and let pace vary: run the climbs 20–40 seconds per mile slower than goal and take back whatever the descent gives you without braking. What you are trying to keep constant is metabolic cost, and pace is only a proxy for it.
Key terms
- Pace
- Elapsed time per unit distance, written mm:ss per mile or per kilometre. The reciprocal of speed.
- Split
- The elapsed time at an intermediate point, or the time taken for one segment. A cumulative split is the clock reading; a lap split is the segment alone.
- Negative split
- Running the second half of a race faster than the first. The pattern behind most personal bests and nearly every distance world record.
- Certified course
- A course measured by an accredited measurer along the shortest possible running line, with a short-course prevention factor added. Only certified courses produce times eligible for records or qualifying standards.
Where pace fits among the other numbers you track
Pace is an output, not a cause. It falls out of how much oxygen you can use, how economically you convert that into forward motion, and what fraction of your maximum you can sustain for the duration of the event. That is why two runners with identical 5 km times can have very different marathon times: the same ceiling, different endurance underneath it.
Use pace with three companions. A race prediction converts a recent result into equivalent times at other distances so your goal is anchored to evidence rather than hope. Heart rate zones tell you whether the pace you have chosen for an easy day is actually easy. And for step-counted walking or mixed walk-run sessions, the steps to miles calculator converts a device's step total into the distance this page needs.
Multisport athletes have one extra wrinkle: swim pace is conventionally quoted per 100 m or per 100 yd rather than per unit of a longer distance, so use the swim pace calculator for that leg and the triathlon finish time calculator to stitch the three splits and transitions into one projected finish.