Resources/Angles: types, measurement, and relationships
Grade 4•Printable worksheet + answer key•CC0 license

Angles: types, measurement, and relationships

A printable lesson on classifying and measuring angles.

Students learn to identify acute, right, obtuse, and straight angles, and solve problems with complementary and supplementary angles.

Print-ready worksheet with answer key and quick teaching tips.

Grade 40 problems10 minAnswer key included
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Ready-to-teach

Clear steps, examples, and practice in one printable page.

Misconception-proof

Highlights common mistakes and how to fix them quickly.

Open license

CC0: free to copy, adapt, and share without attribution.

Quick overview

This free angles worksheet for grade 4 builds understanding of angle types, measurement, and relationships.

Lesson plan snapshot

15-20 min
  • Warm-up (3 min): show examples of angles in the classroom.
  • Model (5 min): demonstrate angle types using a paper corner.
  • Guided practice (5 min): complete problems 1-4 as a group.
  • Independent practice (7 min): finish the remaining problems.

Materials: protractor (optional), pencil, paper corner for reference

Learning targets

  • Classify angles as acute, right, obtuse, or straight.
  • Understand that angle size depends on rotation, not ray length.
  • Find missing angles using complementary (90°) and supplementary (180°) relationships.

Step-by-step approach

  1. 1Compare the angle to a right angle (90°) to classify it.
  2. 2Acute angles are less than 90°; obtuse angles are greater than 90° but less than 180°.
  3. 3For complementary angles, subtract from 90°.
  4. 4For supplementary angles, subtract from 180°.

Common mistakes

Mistake

Thinking longer rays make larger angles.

Try instead

Angle size depends only on the rotation between rays, not their length.

Mistake

Confusing complementary and supplementary.

Try instead

'C' comes before 'S': Complementary = 90° (Corner), Supplementary = 180° (Straight line).

Mistake

Adding instead of subtracting to find the missing angle.

Try instead

If angles add up to 90° or 180°, subtract the known angle from the total.

Worked example

Guided
Two angles are supplementary. One angle is 65°. Find the other angle.
  1. Supplementary angles add up to 180°.
  2. Subtract: 180° - 65° = 115°.
Answer: 115°

Related resources

Geometry

Shape properties and foundations.

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Area & perimeter

Measure rectangles and squares.

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Practice problems

10 problems • 15 min

Printable worksheet
  1. 1
    Two lines intersect forming vertical angles. One angle measures 35°. What is the measure of the angle directly across from it?
  2. 2
    Classify an angle that measures 135°.
  3. 3
    Classify an angle that measures 90°.
  4. 4
    Two lines intersect forming vertical angles. One angle measures 85°. What is the measure of the angle directly across from it?
  5. 5
    Classify an angle that measures 60°.
  6. 6
    Two angles are on a straight line. One measures 115°. What is the other angle?
  7. 7
    Two angles are complementary. One angle measures 45°. What is the measure of the other angle?
  8. 8
    Classify an angle that measures 180°.
  9. 9
    Two angles are on a straight line. One measures 85°. What is the other angle?
  10. 10
    Two angles are supplementary. One angle measures 70°. What is the measure of the other angle?

Answer key

10 answers
  1. 11) 35° (vertical angles are equal)
  2. 22) obtuse
  3. 33) right
  4. 44) 85° (vertical angles are equal)
  5. 55) acute
  6. 66) 65°
  7. 77) 45°
  8. 88) straight
  9. 99) 95°
  10. 1010) 110°

Teacher tips

  • TUse clock hands to demonstrate different angle sizes.
  • THave students find angles in the classroom (door, book, scissors).
  • TPractice estimating before measuring with a protractor.

Parent tips

  • PPoint out angles around the house: corners, partially open doors.
  • PUse a paper corner as a 'right angle checker'.
  • PAsk: 'Is this angle more or less than a right angle?'

Open license

You are free to copy, adapt, and share these materials. No attribution required. Released under Creative Commons CC0 1.0 (public domain).