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Grade 6/Geometry

Radius & Diameter

Calculate radius from diameter and diameter from radius.
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Easy
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8 questions
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8 questions
Medium
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8 questions
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8 questions
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Hard
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8 questions
Prerequisites
Parts of a Circle6 WS
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What to Do Next
Circumference6 WS
The diameter is 2 mm. Find the circumference. Use pi = 3.14.
2 mm

Practice Questions

  1. The radius is 2 cm. What is the diameter?
    Show answer

    4 cm

  2. The diameter is 16 mm. What is the radius?
    Show answer

    8 mm

  3. The radius is 4 mm. What is the diameter?
    Show answer

    8 mm

  4. The radius is 6 cm. What is the diameter?
    Show answer

    12 cm

  5. The diameter is 20 mm. What is the radius?
    Show answer

    10 mm

Quick Tip
Diameter = 2 × Radius. Radius = Diameter ÷ 2.
Teacher Resources
Teaching Notes

This collection focuses on radius & diameter. Use grid paper to help students visualize area and perimeter.

Vocabulary
Radius: Distance from center to edge.
Diameter: Distance across the circle through center.
Common Mistakes
  • Confusing Area and Perimeter formulas
  • Forgetting to double the sides for Perimeter
  • Using wrong units (e.g., cm instead of sq cm for Area)
  • Confusing radius and diameter lengths.
  • Forgetting diameter is 2x radius.
  • Measuring lines not through the center.
  • Incorrectly dividing or multiplying by 2.
Differentiation
SupportHave students trace shapes on grid paper and count squares.
ChallengeChallenge students to find multiple rectangles with the same area but different perimeters.
Discussion Questions
  • What is the difference between Area and Perimeter?
  • Can two rectangles have the same perimeter but different areas?
  • Why do we use 'square' units for area?
  • How are radius and diameter related?
  • Can a radius be longer than a diameter?
  • Where do we see circles in everyday life?
  • What if a line across a circle doesn't go through the center?
Extension Activities
  • Measure the classroom floor area.
  • Design a garden with a specific perimeter.
  • Create art using only rectangles of specific areas.
Parent Tip

Use string to measure the radius and diameter of round objects.

Learning Path
Skill Cluster

Geometry and Measurement

Estimated Time

20 minutes

Skills Practiced
Radius & diameter