Measuring angles with a protractor
Read and draw angles with a protractor. Find angles on a straight line, vertically opposite angles and angle bisectors.
- UK: Year 5
- France: grade 4
- Germany: grade 5
- Iran: grade 4
- Afghanistan: grade 5
- Syria: grade 5
- Palestine: grade 4
- Ukraine: grade 5
- Russia: grade 5
Guide
A protractor is a half circle split into 180 equal parts. Each part is one degree (angle) (1°).
To read an angle: put the centre of the protractor on the vertex and its zero line along one arm. Then read the number where the other arm crosses.
A protractor has two scales. Read the scale that starts at 0 on your first arm. An acute angle is less than 90°; an obtuse angle is more than 90°.
Angles on a straight line add up to 180°. Two angles that add up to 180° are supplementary angles.
When two lines cross, vertically opposite angles are equal.
An angle bisector cuts an angle into two equal angles.
Turn the protractor with your finger, or tap it and use the arrow keys. Near an arm it snaps into place.