Pace Calculator

What this calculator answers

Give it two of distance, finish time and pace, and it works out the third: the pace a goal time needs, the finish time a pace gives, or how far you went. Every answer comes with the pace per mile and per kilometer, the speed in mph and km/h, the halfway time and a split for each mile and kilometer. It is arithmetic on your numbers, not a forecast. To estimate what a recent race says about a different distance, use a race time predictor.

How to use it

• Solve for: the value you want. The other two are the inputs, and the answer appears in the results, never in a box you typed into.
• Race: a 5K, 10K, 15K, 10 miles, half marathon or marathon at its exact distance. Choose Custom distance to type your own in miles, kilometers or meters.
• Finish time: hours:minutes:seconds such as 1:52:30, or minutes:seconds such as 25:00. 3h30m, 45 min and a bare 45 (minutes) work too. A time with two parts is minutes and seconds, as on a stopwatch, and the line under the box says how it was read.
• Average pace and pace unit: minutes:seconds per mile or per km, such as 8:30. Choose mph or km/h to type a treadmill or bike speed instead. When you solve for pace, the unit decides which pace leads the answer.
• Splits: even pace, or Faster second half with a negative split, how much quicker the second half is (1:00 is one minute; a bare number is seconds).

Results update as you type. The Try buttons load a 4-hour marathon, a 10K at 5:30 per kilometer, 45 minutes on a treadmill at 6.5 mph, and the same marathon run as a negative split. To weigh two plans, press Save for comparison, change an input and save again: each saved scenario shows how its pace, time and distance differ from the first. When you switch what to solve for, the box that reappears is filled with the answer you just had (a time or pace rounded to the second), so the numbers on screen still describe one run. After a race pace, Continue in the Race Time Predictor takes the race and your time over to estimate a different distance.

How to calculate running pace

Pace is time divided by distance. Turn the time into seconds first (1 hour is 3,600 seconds, 1 minute is 60), divide, and turn the result back into minutes and seconds. The same relation, rearranged, gives the time or the distance:

For example, time = pace × distance: a 10K at 5:30 per km (330 s) takes 330 × 10 = 3,300 s, which is 55:00.

Speed is the same ratio the other way up, distance over time. With the pace $p$ in seconds per mile (or per km):

• $p$ is the pace in seconds per unit of distance.
• 1 mile is exactly 1.609344 km, so a pace per mile is 1.609344 times the pace per km.

Worked example: a half marathon in 1:52:30

1. Distance: a half marathon is 21.0975 km, and 21.0975 ÷ 1.609344 = 13.1094 miles.
2. Time in seconds: 1 × 3,600 + 52 × 60 + 30 = 6,750 s.
3. Pace per mile: 6,750 ÷ 13.1094 = 514.9 s, which is 8 minutes 34.9 seconds, or 8:35 per mile to the nearest second.
4. Pace per km: 6,750 ÷ 21.0975 = 319.94 s, 5:20 per km.
5. Speed: 13.1094 miles ÷ 1.875 hours = 6.99 mph, or 21.0975 km ÷ 1.875 hours = 11.25 km/h.

At an even pace every mile takes 8:35. Halfway comes at 56:15, the 13-mile marker at 1:51:34, and the last 0.11 mile takes 56 seconds. On a track the same pace is 2:08 per 400 m lap.

Pace per mile vs pace per kilometer

Multiply a pace per km by 1.609344 to get the pace per mile, and divide to go back. Do it in seconds: 5:00 per km is 300 × 1.609344 = 482.8 s, or 8:03 per mile. The other way, 8:00 per mile is 480 ÷ 1.609344 = 298.3 s, or 4:58 per km. The calculator shows both units in every answer, so this table is only for quick reading:

What pace do I need for my goal time?

Divide the goal time by the race distance. These are the exact paces for some round finish times, rounded to the nearest second; for any other time, choose the race and type the time.

A 2-hour half marathon and a 4-hour marathon need the same pace, 9:09 per mile (5:41 per km), because the half is exactly half the distance.

To finish under a goal, run a little faster than the pace shown, because rounding can go either way. A 25:00 5K is 482.8 s per mile, shown as 8:03; running exactly 8:03 per mile finishes in 25:01.

Treadmill speed to pace (mph and km/h)

A treadmill shows speed, and pace is 3,600 seconds divided by it: 6 mph is 3,600 ÷ 6 = 600 s, or 10:00 per mile. Choose mph or km/h as the pace unit to enter a speed directly. Common settings:

In km/h it works the same way: 10 km/h is 3,600 ÷ 10 = 360 s, or 6:00 per km. To find how far a session went, solve for distance: 45 minutes at 6.5 mph is 6.5 × 0.75 = 4.875 miles (7.85 km).

Even and negative splits

An even pace runs every mile in the same time. A negative split runs the second half faster than the first. Enter how much faster, and the calculator divides the finish time into two halves, each run at an even pace:

where $T$ is the finish time and $D$ is the negative split. A 4-hour marathon with a 2-minute negative split has halves of 2:01:00 and 1:59:00: 9:14 per mile (5:44 per km) to halfway, then 9:05 per mile (5:38 per km). The splits table then shows each mile at its own pace. Mile 14, which contains halfway at 13.11 miles, mixes the two and takes 9:06.

Reading the result

• The headline is what you solved for, with the distance and the other input restated so you can check them.
• Check the finish time appears when a time was probably meant in hours. 3:30 for a marathon is read as 3 minutes 30 seconds, a pace of 0:08 per mile; the Use 3:30:00 button changes it in one tap.
• The tiles give the paces and speed you didn’t enter, the time per 400 m (one lap of a standard outdoor track) and the halfway time.
• The splits table has a row per mile and per kilometer, with the time of each split and the elapsed time at its marker. The last row is the part left over, such as 0.11 mile of a half marathon. Download it as a CSV file or print it.
• The “what if” table repeats the calculation nearby. When you solve for pace it lists the pace for finish times either side of yours (1-minute steps around a 25:00 5K, 5-minute steps around a 4-hour marathon). When you solve for time or distance it varies the pace in 5-second steps, or a speed in steps of 0.5 mph or 1 km/h.

Assumptions and limitations

• The distance is the course distance, and a mile is exactly 1.609344 km.
• The pace is even, or even within each half for a negative split. Hills, wind, heat, crowded starts and stops are not modeled.
• Times are rounded to the nearest second for display only. Each split and each elapsed time is rounded on its own, so adding the shown splits can be a second off the elapsed time.
• It does arithmetic on the time you give, not a prediction of the time you can run.

Common mistakes

• Typing 3:30 for three and a half hours. Two-part times are minutes and seconds. Type 3:30:00 or 3h30m, or press the button the calculator offers.
• Using 26.2 miles for a marathon. The marathon is 26.2188 miles. Dividing 4:00:00 by 26.2 gives 549.6 s (9:10 per mile) instead of 549.2 s (9:09), and at 549.6 s the full course takes 4:00:10.
• Reading decimal minutes as seconds. A pace of 8.5 minutes is 8:30, not 8:50. The pace box accepts 8.5 and shows how it read it.
• Converting in the wrong direction. A pace per mile is always longer than the pace per km, so multiply by 1.609344 to go from a pace per km to a pace per mile. For speed, the km/h figure is the larger one: 10 mph is 16.09 km/h.
• Training by your watch’s distance in a race. It usually reads long on a measured course, so its pace flatters you slightly, and you finish later than the watch’s pace suggests.