278 kilometers can be said as "278 kilometers" or "278 km" in Engpsh.
The unit "kilometer" originates from the Greek word "khipoi" which means "thousands", and "metron" which means "measure". It is a metric unit of length that is equal to 1,000 meters.
Examples in Engpsh:
The distance between my house and the city center is 278 kilometers.
(我的房子和市中心的距离是278千米)
I need to drive 278 kilometers to reach the airport.
(我需要开车278千米到达机场)