Running Pace Explained: Convert min/km to min/mi and Predict Your Race Times

Almost every running plan, treadmill display and race goal is written in a unit you might not think in. Your watch shows min/km, the American training plan you downloaded uses min/mi, the gym treadmill speaks km/h, and the race predictor on the start line wants to know your “5K time.” None of these are hard to convert — but doing the arithmetic in your head mid-run is a quick way to get it wrong. This guide explains what pace actually is, how the units relate, and how a single recent result can predict your times across every standard race distance.

Pace versus speed — two views of the same run

Pace and speed are the same information turned inside out. Speed is distance over time (how far you go each hour): 12 km/h. Pace is time over distance (how long each unit takes): 5:00 per km. Runners almost always think in pace because it’s the number you can hold onto during a run — “just keep hitting 5:30s” is easier to pace than “stay at 10.9 km/h.”

The conversion between them is a simple reciprocal. If you run 1 km in 5:00 (300 seconds), your speed is 3600 ÷ 300 = 12 km/h. Going the other way, a 12 km/h pace is 3600 ÷ 12 = 300 seconds = 5:00 per km. Treadmills and cycling computers tend to show speed; running watches show pace; the Running Pace Converter shows all four at once — min/km, min/mi, km/h and mph — so you never have to pick.

Converting between min/km and min/mi

This is the conversion that trips people up most, because a mile is longer than a kilometre, so the pace number gets bigger even though you’re running the same speed. One mile is exactly 1.609344 km. To turn a per-kilometre pace into a per-mile pace, multiply by that factor:

5:00 /km × 1.609344 = 8:03 /mi

So a 5:00/km runner is running roughly 8:03/mi — the per-mile figure is always the larger number. Going from min/mi back to min/km, you divide by 1.609344 instead. A common mistake is to convert the minutes and seconds separately; always convert the total time for the distance (300 seconds, not “5” and “0”) and then reformat into minutes and seconds at the end.

How race-time prediction works

The genuinely useful trick is predicting a race time you haven’t run from one you have. The standard tool for this is Riegel’s formula, published by Pete Riegel in the 1970s and still the basis of most online predictors:

T₂ = T₁ × (D₂ / D₁)^1.06

In plain terms: take your known time (T₁) for a known distance (D₁), scale by the ratio of the new distance to the old, and raise that ratio to the power 1.06. The exponent is the whole story. If endurance were free, the exponent would be 1.0 and you’d hold the exact same pace at any distance. Because we slow down as distance grows, the exponent is slightly above 1.0, which stretches the predicted time for longer races and compresses it for shorter ones.

A worked example: a 25:00 5K predicts a marathon of

25:00 × (42.195 / 5)^1.06 ≈ 3:51

The converter runs this calculation for every standard distance at once — 1 mile, 5K, 10K, half marathon (21.0975 km) and full marathon (42.195 km) — so a single result fills in the whole table.

How much to trust the prediction

Riegel’s formula is accurate to within about ±5% for well-trained runners predicting across similar distances — and every word of that qualifier is load-bearing. The formula can’t see your training log, so it quietly assumes you’ve built the endurance the target distance demands, and it gets shakier the further you extrapolate: a 10K predicted from a half marathon is reliable, a marathon predicted from a single mile is a stretch. Treat the number as a sensible goal-pace starting point, not a guarantee — how to pace a marathon covers how much to discount it when your weekly mileage doesn’t back the prediction up.

Pacing with even splits

Once you have a target pace, the simplest race strategy is even splits — covering each kilometre (or mile) in the same time. The converter lists the cumulative time you should hit at each kilometre, so you can glance at your watch and know instantly whether you’re ahead or behind. At 5:00/km your 10 km split should read 50:00, your 20 km split 1:40:00, and so on.

Even pacing is not just tidy — it’s usually the fastest way to race, and the longer the distance the more it matters. The full case for holding back early, the physiology behind it, and a per-kilometre plan you can actually run are in how to pace a marathon with negative splits.

Putting it together

Plug a recent race or hard effort into the Running Pace Converter and you’ll immediately see your pace in every unit, your speed in km/h and mph, predicted times for every standard distance, and an even-split table to race against. From there you can layer on the rest of training: dial in your easy, threshold and interval paces with the Training Zones calculator, or — if you cross-train on the bike — estimate your speed from power with the Cycling Power to Speed calculator.

General information for training and pacing, not medical or coaching advice. Build mileage gradually and listen to your body.