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
Why This Measuring Trick Works So Well
This is a great tip because accurate cabinet measurements matter more than most people realize. A small error inside a cabinet can snowball into shelves that bind, drawer boxes that rack, or hardware that refuses to line up cleanly. Interior dimensions are especially unforgiving because you are usually fitting rigid parts into a fixed opening. There is no room to cheat a cut once the case is built and installed.
What makes inside measurements tricky is that most tape measures are designed for outside work. The hook, the slight curve of the blade, and the inability to seat the tape fully into a corner all introduce small inaccuracies. Those fractions add up fast, especially when you are working with plywood or prefinished materials that do not tolerate trimming after the fact.
Establishing a solid reference point rather than relying solely on a tape is a valuable trick that improves accuracy across a wide range of woodworking tasks. Turning an inside measurement into a straight pull improves consistency and makes it easier to double-check your numbers before committing to a cut.
Ideas like this endure because they simplify the act of measuring instead of complicating it. A fixed spacer becomes part of the measuring motion itself, something you reach for without thinking once it proves reliable. When measuring feels straightforward and uneventful, the work that follows usually goes the same way.