Angle ruler

An angle ruler is a straightedge or hinged tool used to set, copy, or measure an angle. Common types include a protractor ruler with a printed scale, a sliding T-bevel that captures a corner, a folding template ruler for tracing, and a digital angle ruler with an electronic readout.

Open the ruler’s arms so each one sits flat against a surface of the angle, then read the degrees off the scale where the arms cross — or lock the angle and transfer it to your workpiece. With a digital angle ruler or a phone app, the angle simply appears as a number once the tool is seated.

Yes. The Protractor app works as a digital angle ruler on your iPhone: rest the phone along a surface and it reads the angle from its tilt sensors, no printed scale to misread. An on-screen camera mode lets you measure an angle you can’t place the phone against.

A plain ruler measures length, not angles. To measure an angle you need a ruler with an angle scale (a protractor ruler), a hinged bevel, or a digital angle ruler. A phone app replaces all three by reading the angle from the sensors inside the phone.

For precision, a digital angle ruler beats a printed scale because there’s no eyeballing. For everyday use, a phone app is the most convenient angle ruler — it reads in degrees, percent slope, or ratio, needs no separate batteries, and is always with you. A sliding bevel is still handy when you need to physically transfer an angle to a saw.