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4th grade · Math · Unit 16 of 17

Measuring Angles

Protractors and adding angles

What your child practices

Reading angles on a protractor (including which scale to use), sketching angles of a given size, and finding a whole angle or a missing part by adding and subtracting degrees.

New York State Learning Standards learning standard: NY-4.MD.6; NY-4.MD.7 · measuring and sketching angles in whole degrees with a protractor, and adding and subtracting angle measures to find unknown angles

How we explain it

Children can open this short lesson before they practice.

  1. Put the protractor's middle point on the vertex and line up 0° with one ray.
  2. Read the number the other ray passes, on the scale that starts at 0.
  3. An angle split into parts is the sum of the parts. A square corner is 90°, a straight angle 180°.

Example: A square corner is split into two angles. One is 35°. How big is the other? The two parts add up to 90°. 90 − 35 = 55. Answer: 55°

Measuring Angles in New York

In the New York State Learning Standards, this is unit 16 of 17 in 4th grade Math, after Times as Many and before Tenths & Hundredths.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: New York State Education Department (NYSED)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    About how big is this angle?

    • 60°
    • 30°
    • 120°

  2. Question 2

    One ray of the angle is on 0° of the protractor. The other ray passes 130° on the same scale. How big is the angle?

    • 130°
    • 100°
    • 140°
    • 50°

  3. Question 3

    Three angles make a straight line: 40°, 80° and one more. How big is the missing angle?

    • 120°
    • 40°
    • 60°
    • 50°

  4. Question 4

    To sketch a 90° angle, where does the second ray go?

    • a little past straight up
    • back along the first ray
    • almost flat, close to the first ray
    • straight up from the first ray, making a square corner

  5. Question 5

    A square corner (90°) is split into two angles. One is 35°. How big is the other?

    • 145°
    • 35°
    • 125°
    • 55°

  6. Question 6

    An angle is split into two parts: 30° and 15°. How big is the whole angle?

    • 15°
    • 45°
    • 35°
    • 55°

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