Usage patterns
〈物〉の長さを測るto measure the length of something
Please measure the length of this stick.
長さが〈数〉あるto be a certain length
This rope is five meters long.
長さを調節するto adjust the length
Please adjust the length of the belt.
〈物〉の長さに合わせるto match/fit the length of something
I cut the fabric to match the length of the curtain.