Choose a corner to start and measure the total length of the wall. Continue around the entire room.
Be sure to measure from the outside of the trim edge to the far wall.
When measuring door and window openings, make sure you measure from outside trim edge to outside trim edge.
It’s important that all of your measurements add up to the overall wall measurements.
Also, be sure that all measurements are in inches so, 6′ 3″ should be marked as 75″.