Why a smaller number is faster
Pace (min/km, min/mile) is time per distance, while speed (km/h, mph) is distance per time — the two are reciprocals. So a smaller pace number means a faster pace: 4 min/km is faster than 6 min/km. Double the speed and the pace number halves — the pace↔speed conversion follows a hyperbola. Concretely: km/h = 60 ÷ (min/km).