How to use it
- Choose Work out and the Units you want to read.
- Pick a Race distance, or choose Custom distance and type it in the field that appears.
- Type the two values you know in Pace and Time. The field of the value you are working out is hidden.
- For a plan with a faster second half, choose Negative split under Split and type the Second half faster by percentage.
- Read the Result, the pace and speed boxes, and open Split times for each kilometre or mile to see every split.
How the pace and speed are calculated
Pace is the time divided by the distance, and speed is the distance divided by the time. The three values are linked, so the calculator works out the one you leave out.
A mile is 1,760 yards and a yard is exactly 0.9144 metres, so a mile is exactly 1,609.344 metres. A pace per mile is therefore the pace per kilometre multiplied by 1.609344.
pace = time ÷ distance
time = pace × distance
speed (km/h) = distance (km) ÷ time (hours)
1 mile = 1.609344 km- Times are rounded to the whole second, so a pace can look one second different from the exact value.
Negative split and the split table
A negative split runs the second half faster than the first. The total time stays the same, so the first half is run a little slower. The calculator takes the percentage you enter as q and works out the first-half pace from the total time.
The split table adds up the time at each kilometre or mile, so you can see the plan along the course. The last row is the finish, which can be shorter than a full unit.
first-half pace = 2 × time ÷ (distance × (2 − q))
second-half pace = first-half pace × (1 − q)
q = the second half is faster by this fraction (3 % = 0.03)What this calculator does not cover
- Hills, wind, heat and the start of a race change the time of each split. The table is a plan, not a prediction of your splits.
- A GPS watch can measure a distance that differs from the official course, so its pace can differ from this calculator. Use the official distance when you plan a race time.
- Race distances are the standard lengths set for road races. A course that is measured differently needs its own distance.
Worked example: 10 km in 50:00
Enter 50:00 as the Time and 10 km as the distance, and choose Work out as Pace. The pace is 3,000 seconds ÷ 10 = 300 seconds per kilometre, which is 5:00 per km.
Per mile it is 300 × 1.609344 = 482.8 seconds, which is 8:03 per mile. The average speed is 10 ÷ (3,000 ÷ 3,600) = 12.00 km/h, or 7.46 mph.
With a 3 % Negative split the first kilometre takes 5:05 and the sixth takes 4:55, and the total stays 50:00.
| Even split | Negative split 3 % | |
|---|---|---|
| First kilometre | 5:00 | 5:05 |
| Sixth kilometre | 5:00 | 4:55 |
| Total time | 50:00 | 50:00 |
Frequently asked questions
How do I turn a pace per km into a pace per mile?
Multiply the seconds per kilometre by 1.609344. A pace of 5:00 per km is 300 × 1.609344 = 482.8 seconds, which is 8:03 per mile.
What is the difference between pace and speed?
Pace is the time taken to cover one kilometre or mile, such as 5:00 per km. Speed is the distance covered in one hour, such as 12 km/h. A pace of 5:00 per km is the same as 12 km/h.
What is a negative split?
A negative split is a race or run where the second half is faster than the first. The total time is the same as the average pace gives, so the calculator keeps the total and changes only how it is shared out.
Why does my watch show a different pace from this calculator?
A GPS watch measures the distance by satellite and can record a little more or less than the course. Plan with the official distance, and then compare the total time on your watch with the calculated one.
Is the marathon distance exactly 42.195 km?
Yes, the official marathon distance is 42.195 km, about 26.22 miles. The half marathon is 21.0975 km, about 13.11 miles, which is half of the marathon.
Can I use the calculator for walking or cycling?
Yes. Pace and speed work for any steady activity. For cycling, the speed in km/h is the figure most people use, and the time for a distance follows from it.
Sources
- Wikipedia: Mile (the international mile is exactly 1,609.344 m, or 1,760 yards)
- Wikipedia: International yard and pound (yard 0.9144 m, pound 0.45359237 kg, agreed 1959)
- Wikipedia: Marathon (official distance 42.195 km)
- Wikipedia: Half marathon (official distance 21.0975 km)
Figures and text last checked on Tuesday, November 10, 2026.