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What is a Miter Square?

Terrie Brockmann
Terrie Brockmann

A miter square is one of several types of squares. This instrument is for marking angles to make a miter joint. A miter joint is a corner joint, usually made by abutting two ends that are at 45° angles. Generally, woodworkers use miter squares, but they may be used in any procedure where a worker needs to measure an angle. Some miter squares measure only a 45° angle, while others are adjustable to other angle measurements.

Generally, a mitered joint consists of two 45° angled pieces of material that join and create a 90° angle. A common example is a picture frame. Some mitered joints need to be at different angles, such as a hexagon-shaped picture frame. An adjustable miter square is useful for accurately measuring trim for projects where the angles may not be a perfect 45°. An example of this is older houses where the walls are not flawlessly square.


A person uses a fixed 45° miter square by placing the straight edge against the long side of the board and then marking the board along the square's angled edge. Many squares have a fence or a protruding edge that sets the square tightly against the board. Adjustable miter squares have an arm that swivels to the desired angle. A person holds the straight edge along the board like a fixed miter square and pivots the angled edge to the degree graduation mark of the desired angle. For example, if a person wants a 65° angle, he or she lines up the 65 mark on the board edge; the resulting angle will be 65°.

Manufacturers sometimes combine miter squares with framing squares, try squares, or common squares for efficiency. They are made of steel and aluminum alloys, wood, and other materials. The best squares are made of the strongest materials because they are less likely to warp and lose accuracy. Accurate measuring helps to ensure a tighter joint.

Some companies offer a folding miter square that is conveniently portable. When purchasing a folding square, a buyer should check to see if it holds an angle tightly or if it slips. It is important to have accurate measurements, or the project's quality will suffer.

A Japanese miter square looks like an off-kilter picture frame. This box-like square has 45° angles at both ends. Woodworkers use it to set up saws to cut 45° angles. The square has no gradation markings because it only makes a 45° angle.

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