standard lengths for flatbars/box/angle

hi there, is there a standard defining the lengths of flatbars/box section/angle iron or is every manufacturer free to define his own length?

Many times when i am buying metal for a new project i find the length is different from what i had assumed during the planning stage at home.

thanks,

Sam

Most hot-rolled bar comes in 20 foot lengths Cold rolled often comes in 12 foot lengths, as does a lot of Stainless steel bars.

Tube can be in 20 ft or 24 ft lengths. Pipe comes in 21 ft lengths so you can get 3 pieces 7 ft long.

Big beams and structural shapes come in 40 ft lengths.

Aluminum is a bit wacky coming in 12 ft, 16 ft, 20 ft, 21 ft or 24 ft lengths.

Is pipe in 7 ft lengths used for something in particular?... Thanks - Joe