"km in length" is a correct and usable part of a sentence in written English.
It is typically used to refer to the length of something, such as a road or a river. For example: "The bridge was 5 km in length."
This volcanic island, the second largest of the Canaries, measures 60 miles (100 km) in length.
It averages 138 miles (222 km) in length and 17 miles (28 km) in width.
It is the state's longest river, about 350 miles (560 km) in length.
Istria's highly indented shoreline, 267 miles (430 km) in length, exhibits numerous drowned valleys.
Aguán River, Spanish Río Aguán, river in northern Honduras, 150 mi (240 km) in length.
Only the segment passing through Kansas, all of 13 miles (21 km) in length, remained unaltered.
At 208 mi (335 km) in length, it is Sri Lanka's longest river.
New Horizons also found several deep fractures in Pluto's surface, the largest of which spans more than 200 miles (322 km) in length.
The group comprises 11 well-wooded islets, none of which exceeds 1.5 miles (2.5 km) in length.
Some 1,100 miles (1,800 km) in length, it is the world's longest man-made waterway, though, strictly speaking, not all of it is a canal.
It extends about 13 miles (21 km) in length and 2 to 7 miles (3 to 11 km) in width and is administered as part of Charlevoix county.
