Kilometers to miles is the standard conversion for anything measured in distance rather than length — road signs, driving directions, and race distances published for an international audience. The clearest example is the marathon: its official distance is 42.195 km everywhere in the world, which converts to 26.2188 mi, the figure US and UK runners actually use when they talk about “running 26.2.”
This pair is most useful for one-off distances — a route, a race, a country’s speed limit sign. If you’re trying to convert a running pace (minutes per kilometer to minutes per mile, or the other way around) rather than a fixed distance, that’s a different calculation involving time as well as distance — the running pace calculator handles that conversion directly.
Road and race distances are a good anchor for sanity-checking any km-to-mi conversion: a 10 km race is about 6.2 mi, and a half marathon’s 21.0975 km comes out to roughly 13.11 mi — a little more than double a 10K, since the half marathon distance itself is slightly more than 20 km.