To measure an angle means to measure the size of the space or opening created between the two rays. This is measured using a special tool called a protractor.

• Angles are measured using a unit called degree.
• A degree is denoted by the symbol “o” just like in 90°, 180° or 360°.
• A protractor is one of the most important geometric tools as it helps in measuring angles in degrees.

When we look at a protractor, we can see measurements from 0 to 180 from left to right at the outer edge and 0 to 180 from right to left on the inner edge. The measurements in both the edges add up to 180°. For example the protractor on the right reads m∠STV = 50° and m∠DTV = 130° [Note that 50° + 130° = 180°]