Measuring Angles

Measuring Angles

Basic, GCSE(F),

Angles are measured using a protractor. A protractor measures in degrees. A protractor is normally a semi-circle (as found in geometry sets) or a complete circle.

There are four basic steps to measuring an angle accurately using a protractor.

1. Place the centre of the protractor (the middle of the bottom line, normally shown with a circle) exactly on the point of the angle being measured:

2. Make sure that the base line of the protractor is exactly on top of one of the lines of the angle:

3. Check if the inner scale (of numbers) or the outer scale is being used by determining which scale is at 0º on the line:

4. Read the angle measurement from the correct (inner or outer) scale:

In this instance, the angle being measured is 42º

Examples

1. What is the size of the angle being measured below?

Answer: 55º

The zero is on the inner scale. Reading from the zero, read an angle of 55º.

2. What is the size of the angle being measured, below?

Answer: 132º

The zero is on the outer scale. Read round the outer scale to 132º.