How to use the marathon pace calculator
- Pick I know my goal time or I know my pace.
- Choose the Race distance, from 1 mile to the marathon, or enter a custom distance in km or miles.
- Enter your Goal finish time in hours, minutes and seconds, or your Target pace per mile or per km.
- Read the finish time, paces and speed, then choose Show splits every mile or kilometer. Copy splits copies the list.
- To set a goal from a recent result, use the predictor, then press Plan marathon splits.
How the calculator works
Pace is time divided by distance. The calculator uses 1 mile = 1.609344 km, a marathon of 42.195 km (26.21875 miles, the distance World Athletics standardized in 1921) and a half marathon of exactly half that, 21.0975 km. Splits assume an even pace, so the elapsed time at a mark is the finish time times the share of the distance covered. Seconds are rounded once, at the end, so a pace never shows as 5:60.
The predictor uses Pete Riegel's formula: T2 = T1 × (D2 / D1)^1.06, where T1 is your recent time, D1 its distance and D2 the distance you want to predict.
Worked example
The starting inputs are a 4:00:00 marathon. That is 14,400 seconds over 26.21875 miles, or 549.2 seconds per mile, shown as 9:09 per mile. Over 42.195 km it is 341.3 seconds, shown as 5:41 per km, and the speed is 6.55 mph (10.55 km/h). With mile splits you pass Mile 1 at 9:09, Mile 10 at 1:31:32 and the half marathon at 2:00:00, then finish at 4:00:00. In the predictor, a 25:00 5K gives 52:07 for a 10K, 1:55:00 for a half marathon and 3:59:47 for a marathon.
Limits and edge cases
Real races are not even. Hills, heat, wind and crowds change your pace, and your watch usually records a little more than the certified distance, so watch pace can look faster than the pace here. The Riegel formula is built from world-record data and works best between roughly the mile and the marathon. It rejects out-of-range entries and paces faster than 1:30 per km or slower than 2 hours per km. Related tools: the heart rate zones calculator for easy and tempo effort, the calorie burn calculator for fueling long runs, and the speed converter for mph, km/h and m/s.
Frequently asked questions
What pace do I need to run a 4 hour marathon?
You need an even pace of 9:09 per mile, or 5:41 per kilometer, which is 6.55 mph. At that pace you reach the half marathon mark in 2:00:00.
How do I convert pace per kilometer to pace per mile?
Multiply the pace in seconds per kilometer by 1.609344 to get seconds per mile. For example, 5:41 per kilometer is 341 seconds, and 341 × 1.609344 = 548.8 seconds, or 9:09 per mile. To go back, divide.
Can I predict my marathon time from my 5K?
You can get a rough number with the Riegel formula. A 25:00 5K predicts a 3:59:47 marathon, but that assumes you train for the marathon as well as you did for the 5K. Runners without long runs usually finish slower, so a half marathon result is a better base.
Should I run even splits or negative splits in a marathon?
Even pace, or a slight negative split where the second half is a little faster, is the usual coaching advice, because starting too fast tends to cost more time late in the race than it saves early. This calculator shows even splits as your baseline.
How many miles is a marathon exactly?
A marathon is 42.195 kilometers, which is 26 miles 385 yards or 26.21875 miles. World Athletics standardized the distance in 1921, and the calculator uses it for all paces and splits.
Sources: World Athletics, marathon; Riegel, American Scientist 69(3), 1981. General fitness information, not medical advice.