Mark the positions you want the wire shelving on the wall with a sharpened pencil.
Check the height of the marks with the measuring tape to ensure they are the same distance from the floor. This allows you to obtain the most accurate measurements.
Stretch the measuring tape across the marks in the space you want to add the shelving.
Ask someone to hold one end of the measuring tape while you stretch it to the other wall or space you require the shelves.
Subtract 3/4 inch from the measurement. This allows one end to touch the wall. If you want the wire shelving to touch both walls, subtract 1 1/2 inches.
Jot down the measurements on a piece of paper. This is particularly important if you are purchasing several wire Rubbermaid shelves in different lengths. Take the measurements with you to order the shelving.