L-Shaped Rulers: Checking a Right Angle in Patternmaking

Eight Needles Journal · Measuring

An L-shaped ruler gives you a convenient right-angle reference. It can help establish a baseline and check rectangular details, but it should be aligned to a deliberate reference line rather than the nearest edge of the paper.

Bunka – Multi-purpose L Shaped Ruler. Photo from the Eight Needles collection.

Choose the baseline

Find the centre line, grainline or other reference specified by the drafting method. Place one arm of the ruler along it and use the other arm to establish the perpendicular. A cut paper edge may be convenient, but it is not always square.

Check before extending

Make a short light line first. Confirm the ruler has not shifted, then extend with a straight ruler if needed. Repeated small errors at the start of a draft can make later measurements difficult to reconcile.

Use a second check

For a rectangle, check the opposite sides and compare its diagonals before cutting. This can reveal a shape that looks square at one corner but has drifted elsewhere. Keep all measurements in the same unit throughout the check.

A practical example

You are drafting a rectangular pocket. Establish the first right angle from a deliberate baseline, then check the opposite edges and diagonals. If only one corner has been checked, the far edge can still drift. Correct the paper while the lines remain light and easy to revise.