I find that taking inside measurements of a cabinet using a common tape rule can be iffy because the tape won’t bend completely into a corner for a dead-on read. To get an accurate measurement, I incorporate a stick of wood cut precisely to an easy-to-add length, such as 10". Holding one end of the stick against one cabinet side, I extend the tape to the opposite cabinet side and note the measurement at the extended end of the stick. Adding 10" to that measurement gives me the precise interior width of the cabinet.
—Paul Kellam, Visalia, California