A trim guy in Tulsa showed me the 3-4-5 trick works on walls too, not just corners

Patricia Black · 2026-10-10T00:45:04.788436+00:00

I always thought the 3-4-5 method was just for squaring up a deck frame or checking a corner before you pour concrete. Then last month I was helping a buddy frame a closet in Tulsa and an old trim guy named Ray showed me you can use it to check if a wall is actually plumb along its whole length, not just at the ends. He measured 3 feet up from the floor, 4 feet across, and the diagonal was off by almost an inch on a wall that looked fine to me. Has anyone else used this on interior walls or is it mainly a foundation thing?

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A trim guy in Tulsa showed me the 3-4-5 trick works on walls too, not just corners | Carpenters - The Community Guide