Running pace explained: converting pace, speed and race times, and what pace to train at

Runners talk in pace — minutes per kilometre or per mile — rather than speed, because pace multiplies straight into a finish time: 5:00/km × 10 km = 50 minutes. The arithmetic is simple and the conversions are fiddly enough that the pace calculator earns its keep; this guide covers what pace tells you and how to use it for racing and training.

Pace, speed and time

Pace is time per distance; speed is distance per time; they are reciprocals. 6:00/km is 10 km/h; 5:00/km is 12 km/h; 4:00/km is 15 km/h. Given any two of pace, distance and time, the third follows: 21.1 km at 5:30/km takes 1:56:03; a 25-minute 5K is 5:00/km. Treadmills usually display speed, watches display pace, and race results give time — the calculator moves between all three.

min/km to min/mile and back

A mile is 1.609 km, so multiply a per-km pace by 1.609 for per-mile: 5:00/km is 8:03/mile; 6:00/km is 9:39/mile; 4:30/km is 7:15/mile. Going the other way, divide. Common anchors: 8:00/mile ≈ 4:58/km; 10:00/mile ≈ 6:13/km. Keep the seconds straight — 5:30 is 5.5 minutes, not 5.3 — which is where hand calculations go wrong.

Predicting race times

Speed falls as distance rises, in a fairly consistent way for trained runners. Riegel's formula (1981): T₂ = T₁ × (D₂ ÷ D₁)^1.06. A 50-minute 10K predicts a half marathon of 50 × 2.11^1.06 ≈ 1:50 and a marathon around 3:50. The prediction assumes appropriate training for the longer distance; most first marathoners run slower than the formula because their endurance doesn't yet match their speed, so treat the marathon figure as a ceiling. Race-pace tables from Daniels and McMillan refine this; the calculator uses Riegel.

Splits, and running them even

A split is the time for each segment — each kilometre or mile. Even splits (the same pace throughout) or slight negative splits (second half faster) produce the best times in almost every distance; going out fast feels free for two miles and costs far more later, because effort above threshold accumulates fatigue that never repays. Plan the target pace, print or memorise the cumulative splits at each marker (the calculator lists them), and hold back in the first quarter. Chip timing, GPS drift and course measurement mean your watch's distance will read slightly long — run to the course markers, not the watch.

Training paces

Most runs should be easy: 60–90 seconds per km slower than 10K race pace, conversational, in heart-rate zone 2 (Heart rate zones explained: how they're calculated and what each one trains). Tempo runs sit around the pace you could hold for an hour, roughly 10K to half-marathon pace, for 20–40 minutes. Intervals at 3K–5K pace with recoveries build speed; long runs at easy pace build endurance. The mistake nearly everyone makes is running easy days too fast; if in doubt, slow down. The speed-distance-time calculator handles cycling and walking; the interval timer times the reps; the calorie calculator estimates the fuel.