The conversion factor
1 miles per hour equals 1.609343 kilometers per hour. Multiply your miles per hour value by 1.609343 to get kilometers per hour; divide to go back. For the reverse direction, use the kilometers per hour to miles per hour converter or the full speed converter.
Where this conversion comes up
Mixing metric and imperial is a daily reality in travel, shipping, recipes, fitness apps, and spec sheets — this page gives the exact factor plus a scannable table for the values people actually need.