Pace, Time and Distance
All three are the same relationship rearranged. Fix any two and the third follows. The one thing that trips people up is that pace is written in minutes and seconds, not decimal minutes — 8:30 per mile is 8.5 decimal minutes, not 8.3.
Formula
Time = Pace × Distance
Distance = Time ÷ Pace
How Race Prediction Works
The predicted times come from a formula published by Pete Riegel in 1977 and still the most widely used model in endurance running:
The exponent 1.06 encodes a simple observation: doubling the distance costs slightly more than doubling the time, because you cannot hold the same intensity for longer. If the exponent were 1.0, a 20-minute 5K would predict a 40-minute 10K. In practice it predicts about 41:40, and that extra 100 seconds is the fatigue penalty.
The model has a real limitation worth knowing. It assumes you are trained for the target distance. A runner with a sharp 5K time who has never run further than 10 miles will not hit the predicted marathon time, because the marathon is limited by endurance and fuelling rather than by speed. Treat the 5K and 10K figures as reliable, and the marathon figure as a ceiling you have to earn with long runs.
Using Pace in Training
Easy pace
Roughly 1:30–2:00 per mile slower than 10K pace. Should feel conversational. Most distance runners do the large majority of their weekly mileage here, and running it too fast is the most common training error.
Threshold pace
Close to the pace you could hold for about an hour of hard racing — near 10-mile to half marathon pace for most runners. Comfortably hard: sustainable, but not conversational.
Interval pace
Around 3K to 5K race pace, run in repetitions with recovery between. Used to raise aerobic ceiling rather than endurance.