You need to measure the INSIDE width of your locker- most school lockers are 9" or 12" or 15" wide ( there are some 7.5" and 18"). There are NO in between sizes ( e.g. 9.5") so you don't need an exact measurement. An 8.5 x 11″ piece of paper serves as an excellent measurement reference
Lockers also come in 1, 2, and 3-tier variations. The double shelf fits 1 and 2 tier lockers and the single shelf and mini-double fit all 3 locker styles.
LockerShelf™ is not freestanding and gets its strength and durability from the walls of the locker so it is important that you choose the right width when ordering.