Measuring angles in degrees
In a nutshell
An angle is formed when two lines meet at a shared point. Angles are measured in degrees (°), which can be measured with a protractor.
Angles and measurement
The degree (°) is the unit of measurement for angles. There are 90° in a right angle, and 360° in a full circle. A protractor is a tool used to measure how many degrees are in an angle.
Acute angles
Here are the steps for how to measure an acute angle with a protractor:
Procedure
1. | Place the midpoint of the protractor on the vertex of the angle. |
2. | Line up one side of the angle with the zero line of the protractor (where the number 0 appears). |
3. | Read the degrees where the other side of the angle crosses the number scale. |
In the example above, the acute angle has a measurement of 40°.
Obtuse angles
Here are the steps for how to measure an obtuse angle with a protractor:
Procedure
1. | Place the midpoint of the protractor on the vertex of the angle. |
2. | Line up one side of the angle with the zero line of the protractor (where the number 0 appears). |
3. | Read the degrees of the other side of the angle, and subtract this value from 90°. |
4. | Add the 90° to the previous value to find the overall obtuse angle. |
In the example above, the obtuse angle has a measurement of 110° because:
(90°−70°)+90°=110°
Reflex angles
Here are the steps for how to measure a reflex angle with a protractor:
Procedure
1. | Place the midpoint of the protractor on the vertex of the angle. |
2. | Measure the smaller angle on the other side of the reflex angle, with the same method as described above for an obtuse angle. |
3. | Subtract this smaller angle from 360° to give the value of the reflex angle. |
In the example above, the reflex angle has a measurement of 320° because:
360°−40°=320°