Convert minute per mile to second per kilometer

Runners think in pace, minutes per kilometre or per mile, which is the reciprocal of speed: 5:00 min/km is 12 km/h, 6:00 min/km is 10 km/h, and 8:00 min/mile is 12.1 km/h. A 4-hour marathon needs 5:41 min/km, a 25-minute 5 km 5:00 min/km. Swimmers use seconds per 100 m; treadmills usually display km/h or mph, so the conversion comes up on every gym visit. Note that pace is the only unit here where a smaller number means faster.