Math - 2018-19

5.12 - Classify and Measure Angles

The student will 

  • classify and measure right, acute, obtuse, and straight angles.

Adopted: 2016


  • So that I can build a sturdy skateboard or bike trick ramp using the correct angle
  • So that a pilot can use their knowledge of angles to fly and land a plane correctly
  • So that a football player can throw a pass at the correct angle so the receiver can catch the ball  
  • So that when I park a car, I can park it correctly between the lines


  • Angles can be classified as right, acute, obtuse, or straight according to their measures. 
  • Angles are measured in degrees.  A degree is 1/360 of a complete rotation of a full circle.  There are 360 degrees in a circle.
  • To measure the number of degrees in an angle, use a protractor or an angle ruler.
  • A right angle measures exactly 90 degrees.
  • An acute angle measures greater than zero degrees but less than 90 degrees.
  • An obtuse angle measures greater than 90 degrees but less than 180 degrees. 
  • A straight angle measures exactly 180 degrees.
  • Before measuring an angle, students should first compare it to a right angle to determine whether the measure of the angle is less than or greater than 90 degrees.
  • Students should recognize angle measure as additive. When an angle is decomposed into nonoverlapping parts, the angle measure of the whole is the sum of the angle measures of the parts.
  • Students should understand how to work with a protractor or angle ruler as well as available computer software to measure and draw angles and triangles.


The student will use problem solving, mathematical communication, mathematical reasoning, connections, and representations to

  • Classify angles as right, acute, obtuse, or straight.
  • Identify the appropriate tools (e.g., protractor and straightedge or angle ruler as well as available software) used to measure and draw angles.
  • Measure right, acute, obtuse, and straight angles, using appropriate tools, and identify their measures in degrees.
  • Solve addition and subtraction problems to determine unknown angle measures on a diagram in practical problems.


Updated: Mar 06, 2019