Square check calculator

How this square check calculator works

A square layout check uses the Pythagorean theorem. Enter the two side lengths, and StructCalc calculates the exact diagonal. Measure the diagonal in the real layout and compare the two numbers to see how close the frame, wall, deck or foundation is to square.

This is the same idea as a 3-4-5 triangle, just scaled to the actual dimensions on the job. It is useful for checking plates, batter boards, deck frames, openings and any rectangular layout where a small diagonal error can turn into a visible problem later.

For foundation layout, start by setting the longest sill plate or baseline as your reference. Measure out the shorter side from that line, use the calculator to get the exact diagonal, then pull the opposite corner until the diagonal matches. Once the diagonal is right, the corner is square to your reference line.

Example diagonal check

For a 2400 mm by 3200 mm layout, the expected diagonal is 4000 mm. Mark your two sides from the reference corner, then adjust the free corner until the tape reads 4000 mm diagonally before fastening, bracing or pouring.

Need this on site?

StructCalc for Android includes square check alongside stair, rafter, baluster, raked wall and measurement calculators. It is built for fast field input, clear results and offline use when a browser is not the right tool.