Grade 5geometryOriginal practice

Geometry: Circle Radius, Diameter, and Circumference Relationships

Calculate radius from diameter and diameter from radius using d = 2r. Authentic geometric circle diagrams with complete answer key.

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Grade 5 · math

Geometry: Circle Radius, Diameter, and Circumference Relationships

Name Date

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Grade 5 · math · continued

Geometry: Circle Radius, Diameter, and Circumference Relationships

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Look at each circle diagram below and solve for the missing radius or diameter measurement.

1.Look at the circle diagram below with radius r = 7 cm. What is the length of its diameter?

A3.5 cm

B14 cm

C21 cm

D49 cm

Working

2.Look at the circle below with diameter d = 18 in. What is its radius?

A9 in

B36 in

C12 in

D6 in

Working

3.A circular pond has a radius of r = 12 m. What is the total diameter across the pond?

A6 m

B18 m

C24 m

D144 m

Working

Grade 5 · math · Answer key

Geometry: Circle Radius, Diameter, and Circumference Relationships

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Grade 5 · math · Answer key · continued

Geometry: Circle Radius, Diameter, and Circumference Relationships

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Look at each circle diagram below and solve for the missing radius or diameter measurement.

1.Look at the circle diagram below with radius r = 7 cm. What is the length of its diameter?

B. 14 cm

Diameter = 2 × radius = 2 × 7 cm = 14 cm.

2.Look at the circle below with diameter d = 18 in. What is its radius?

A. 9 in

Radius = diameter ÷ 2 = 18 in ÷ 2 = 9 in.

3.A circular pond has a radius of r = 12 m. What is the total diameter across the pond?

C. 24 m

Diameter = 2 × radius = 2 × 12 m = 24 m.

About this practice

Grade 5 · math · Matching answer key included · US Letter and A4

US Letter practice PDF ↓ · Answer PDF ↓A4 practice PDF ↓ · Answer PDF ↓

Preview the original practice

Geometry: Circle Radius, Diameter, and Circumference Relationships: first student practice page

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Teaching guide, sample answers and curriculum references

Before you begin

Identify a circle's center and distinguish a radius from a line across the whole circle.

How to use this worksheet

Model the target skill: define radius as a line segment from the center of a circle to any point on its boundary. Use the first task as a guided example before asking for an independent response.
Check readiness first: Identify a circle's center and distinguish a radius from a line across the whole circle.
Discuss an incorrect response using this distinction: Diameter is twice the radius; a circumference formula requires the quantity named in the question.

A common mistake to discuss

Diameter is twice the radius; a circumference formula requires the quantity named in the question.

What to practice next

Label a circle with both radius and diameter and explain their relationship.

Sample question and answer

Look at the circle diagram below with radius r = 7 cm. What is the length of its diameter?

A. 3.5 cm
B. 14 cm
C. 21 cm
D. 49 cm

Answer: B. Diameter = 2 × radius = 2 × 7 cm = 14 cm.

The corresponding diagram is shown in the practice preview and PDF.

Intended curriculum references: CCSS.MATH.CONTENT.5.G.B.3 · CCSS.MATH.CONTENT.5.G.B.4. These references describe learning goals; they are not endorsements.

Published 2026-10-02; updated 2026-10-02. Original MakeWorksheet practice. Automated consistency checks support publication; independent subject-specialist review is not recorded. Read our editorial policy.