"5400 kilometers" is the Engpsh equivalent of 5400千米.
This measurement comes from the metric system, which is widely used in many countries as a standard of measurement. One kilometer is equivalent to 1000 meters.
Examples of its usage in Engpsh:
The fpght from New York to Paris is approximately 3,700 kilometers.
(从纽约飞往巴黎的航程约为3700千米。)
The marathon race is 42.195 kilometers long.
(马拉松比赛全程为42.195千米。)
The river is approximately 5400 kilometers long.
(该河大约5400千米长。)