In more detail
Pace is time / distance and speed is its reciprocal: a pace in minutes per kilometre converts to km/h as 60 / pace. To go from per-kilometre to per-mile pace, multiply by 1.609344. Paces are written as minutes and seconds, not decimals, so 5.5 minutes is 5:30. Race times for other distances are often predicted with Riegel's formula, T₂ = T₁ × (D₂ / D₁)^1.06.
Why it matters
Runners plan training and races by pace, and GPS watches display it live. A lower pace means faster running, which is the opposite of speed and a common source of confusion. Treating decimal minutes as seconds (5.5 as 5:50) is a frequent slip. Predictions assume you have trained for the longer distance; marathon estimates from a 5 km time are often optimistic.
Example
5 km in 25:00 → 25 / 5 = 5:00 per km = 60 / 5 = 12 km/h
Per mile: 5.00 × 1.609344 = 8.05 min ≈ 8:03 per mile
Marathon at 5:00 per km: 42.195 × 5 = 210.98 min ≈ 3:30:59
Riegel, 10 km from a 25:00 5 km: 25 × 2^1.06 = 52.12 min ≈ 52:07
Common confusion
Pace and Speed carry the same information upside down: 5:00 per km and 12 km/h describe the same run.