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Measuring Angles

Measuring Angles

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:

Measuring an angle: place the centre of the protractor on the point

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

Measuring an angle: make sure the protractor runs along the line

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

Measuring an angle: identify the correct scale to use

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

Measuring an angle: : read the measurement from the correct scale

In this instance, the angle being measured is 42º

Example 1

What is the size of the angle being measured below?

Measuring an angle of 55 degrees

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

Answer: 55º

Example 2

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

Measring and angle of 132 degrees

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

Answer: 132º