Meters to kilometers (m to km)

One meter is exactly 0.001 kilometers, by the meaning of the prefix. There is nothing to look up and nothing that could be revised.

Worked through: 1,000 m x 0.001 = 1 km.

Going the other way, one kilometer is 1,000 meters.

For mental arithmetic: Move the decimal point three places left.

The conversion that running and cycling live on. Track distances are quoted in meters up to 10,000 and in kilometers above it, so a 5,000 m race and a 5 km race are the same distance under two naming conventions. The exception is the road: a 5 km course is measured along the road and a 5,000 m race is run on a 400 m track, so they are the same length and not the same event. The marathon is 42.195 km, which is 42,195 meters exactly and is a number no round figure in either unit explains.

Precision is worth matching to the input. A measurement given as 100 m carries one or two significant figures, and reporting its conversion to six implies a precision the original never had.