# How to Use a Protractor

## What is a Protractor

## Using a Protractor to Measure an Angle

### Find the Vertex or Center Point of an Angle

### Place the Protractor Origin Over the Vertex

Locate the origin near the straight edge of the protractor and in the center. There is usually a hole or circle marking the origin with vertical and horizontal cross-hairs to align the origin on the vertex perfectly. Align the horizontal edge of the origin with one of the edges of the angle so that the other edge of the angle extends to the measurements along the curved edge, as shown in the image above.

### Find the Angle in Degrees

#### Find the Acute Angle

An acute angle is the smaller angle where a line meets another, or technically any angle that is less than 90°. If a line were to meet another line forming two angles, the acute angle would be the smaller angle. With the origin of the protractor aligned over the vertex of the angle and the horizontal edge aligned with one of the lines, find the tick mark along the curve where the line meets. If the acute angle is on the left the tick mark will be on the outside, or outer-most edge, of the protractor. If the acute angle is on the right then the tick mark will be on the inside of the curve.

#### Find the Obtuse Angle

An obtuse angle is the larger angle where a line meets another, or technically any angle that is more than 90°. If a line were to meet another line forming two angles, the obtuse angle would be the larger angle. With the origin of the protractor aligned over the vertex of the angle and the horizontal edge aligned with one of the lines, find the tick mark along the curve where the line meets. If the obtuse angle is on the left the tick mark will be on the outside, or outer-most edge, of the protractor. If the obtuse angle is on the right then the tick mark will be on the inside of the curve.

### Useful Angle Tools

If you need a protractor you can download and print our printable protractor.