📋 In This Guide
Pace, Speed, and Why Runners Think Differently From Cyclists
Runners almost universally think in pace — minutes per kilometer or mile — while cyclists and general fitness trackers more often think in speed — kilometers or miles per hour. Both describe the same underlying rate, just inverted: a faster pace (fewer minutes per km) corresponds to a higher speed (more km per hour). This calculator converts between them instantly either way.
Pace
Minutes per kilometer or mile — how runners naturally think
Speed
Distance covered per hour — useful for treadmills and cycling
Race Prediction
Estimate finish times at other distances from one known result
How Riegel's Race Time Prediction Works
Developed by engineer and running researcher Peter Riegel in 1977, this formula remains the most widely used method for predicting race performance at one distance based on a known result at another. It correctly accounts for something a simple linear projection misses: runners naturally slow down over longer distances due to fatigue, fueling needs, and pacing strategy.
The exponent of 1.06 (rather than 1.0, which would imply maintaining identical pace) is what builds in the realistic slowdown — the further above 1.0 the effective multiplier climbs, the more the prediction accounts for endurance limitations at greater distances.
How Accurate Is Race Prediction, Really?
Riegel's formula tends to be reasonably reliable for predicting races that aren't drastically different in distance from your known result — for example, predicting a 10K time from a recent 5K. Predictions become progressively less certain across very large distance jumps, such as projecting a full marathon from a 5K result, since factors like fueling strategy, mental endurance, and race-day pacing discipline become increasingly influential at longer distances in ways a pure mathematical formula can't capture.
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Worked Example
Notice the pace naturally slows across the predictions — the marathon prediction works out to roughly 5:41/km, noticeably slower than the 5:00/km pace of the original 5K, reflecting Riegel's built-in fatigue adjustment.
5 Pacing Tips for Race Day
Frequently Asked Questions
Divide your total time by the distance covered. Running 5km in 25 minutes gives a pace of 5 minutes per kilometer. This calculator does this automatically and converts between km and miles.
Uses Riegel's formula: predicted time equals known time multiplied by the ratio of target to known distance, raised to the power of 1.06 — accounting for natural slowdown over longer distances.
Runners can't sustain 5K pace over a marathon due to fatigue and fueling demands. Riegel's 1.06 exponent builds in this natural slowdown compared to a straight linear projection.
Reasonably accurate for races not dramatically different in distance from your known result. Less reliable across very large distance jumps, like predicting a marathon from a very short race.
Depends entirely on individual fitness and goals. Many beginner programs target a conversational pace, often around 7-9 minutes per kilometer, though this varies significantly by individual.
Pace expresses time to cover a fixed distance, like minutes per km. Speed expresses distance covered per unit time, like km per hour — the more common format for cycling.
No. All calculations happen instantly inside your browser using JavaScript. Nothing you enter is uploaded, logged, or stored on any server.