Running Pace Calculator
Work out your running pace, finishing time, or distance from any two of the three. Results come in both min/km and min/mile, and a built-in Riegel predictor estimates your time at a new race distance from a recent result.
Your result will appear here
Enter any two of pace, time, and distance, then click calculate.
Quick Answer
Pace equals time divided by distance, time equals pace times distance, and distance equals time divided by pace. Enter any two and this calculator solves for the third, showing pace per km and per mile plus speed. The Riegel formula predicts a race time at a new distance: T2 = T1 × (D2 / D1)^1.06.
How It Works: Formula & Variables
Pace, time, and distance are three views of one relationship, so knowing any two gives you the third. Speed is just distance over time expressed the other way around.
pace = time ÷ distance
time = pace × distance
distance = time ÷ pace
Riegel prediction: T2 = T1 × (D2 / D1)^1.06
1 mile = 1.609344 km
- Pace vs speed
- Pace is time per distance, so a lower number is faster. Speed is distance per time, so a higher number is faster.
- Half marathon
- 13.1 miles, or exactly 21.0975 km.
- Marathon
- 26.2 miles, or exactly 42.195 km.
- Riegel range
- Most reliable for efforts of about 3.5 to 230 minutes; it overestimates at very long distances.
Source: Peter Riegel's endurance prediction model, first published in Runner's World (1977) and later in American Scientist (1981). Peter Riegel.
Worked Examples
Example 1: Pace from a 5K time
A 5K run in 25:00 is a pace of 25 ÷ 5 = 5:00 min/km. Converted to miles, 5 km is 3.10686 mi, so the pace is 25 ÷ 3.10686 = about 8:03 min/mile.
Example 2: Predicting a marathon from a 10K
A 10K in 50:00, predicting the marathon. The distance ratio is 42.195 ÷ 10 = 4.2195, and 4.2195^1.06 ≈ 4.601. So T2 = 50 × 4.601 ≈ 230 minutes, roughly a 3:50 marathon. Keep in mind that Riegel typically overestimates at marathon distance, so read this as an optimistic target rather than a promise.
Key Concepts
Pace and speed are inverses: pace counts up as you slow down, speed counts up as you get faster. They describe the same run from opposite directions.
Units have to match: a distance in kilometers and a pace in min/mile will not line up unless one is converted first. This tool handles that for you and always shows both.
Riegel scales effort, not fatigue: the prediction assumes even, well-trained pacing. Real races add heat, hills, and the wall, which is why long predictions read fast.
Pairs well with heart rate: to train by effort as well as pace, check your zones with the Target Heart Rate Calculator.
Common Mistakes
Mixing units: entering a distance in kilometers while expecting a min/mile pace, without converting, gives a wrong answer. Pick a unit and let the tool convert.
Trusting a prediction out of range: a Riegel estimate far outside the 3.5 to 230 minute window, or from a distance nothing like the target, is unreliable.
Confusing pace with speed: lower pace means faster, higher speed means faster. Reading one as the other flips your sense of how the run went.
Rounding the race distances: a half is 21.0975 km and a full is 42.195 km, not 21 and 42. Those small gaps add up over the full distance.
Frequently Asked Questions
Divide your time by the distance. Run 5 km in 25 minutes and your pace is 25 ÷ 5, which is 5:00 per kilometer. The same math works in reverse: multiply pace by distance to get a finishing time, or divide time by pace to get distance.
They measure the same thing, time to cover one unit of distance, just over a different unit. One mile is about 1.609 km, so a per-mile pace always looks slower on the clock than the matching per-kilometer pace because a mile is the longer distance. This calculator shows both at once.
Yes. The Riegel formula, T2 = T1 × (D2 ÷ D1) raised to the power 1.06, estimates a finishing time at a new distance from a recent race result. Enter your known race and a target distance, and the predictor does the rest.
They work best for efforts lasting roughly 3.5 to 230 minutes. Outside that window they drift, and the 1.06 exponent tends to overestimate at very long distances, so a predicted marathon time from a 10K usually reads a little optimistic. Use it as a target range, not a guarantee.
5K and 10K are the common short races. A half marathon is 13.1 miles or 21.0975 km, and a full marathon is 26.2 miles or 42.195 km. Those last two are not round numbers, which is a frequent source of small errors, so this tool has them built in as presets.
Yes. The distance, time, and pace relationships are the same for any steady activity, so you can work out walking pace, cycling speed, or the time a route will take just as easily as a run.
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Medical disclaimer
For educational purposes only — not professional medical or nutrition advice. Consult a qualified professional before making dietary or exercise changes.
Source: Peter Riegel endurance prediction model (Runner's World 1977, American Scientist 1981).