Around and Across: Radius, Diameter and Circumference

About This Resource

A complete Grade 6 math pack on the parts of a circle. Students label the center, radius, diameter and circumference, use d = 2r and r = d ÷ 2, discover pi by measuring round objects, calculate circumference with C = πd and C = 2πr using π ≈ 3.14 and solve real-life problems about wheels and tracks. Includes slides with worked examples, a lesson plan, worksheet, quiz, homework, flashcards, a rubric and answer keys.

Overview

Students learn the vocabulary of circles: the center, the radius (from the center to the edge), the diameter (all the way across through the center) and the circumference (the distance around). The diameter is always twice the radius. By measuring the circumference and diameter of round objects such as cups, plates and coins, students discover that the circumference is always a little more than three times the diameter. This number is pi (π), about 3.14. Students use C = πd and C = 2πr, round sensibly and apply the formulas to wheels, running tracks and circular gardens.

Resource Details

Subject: Math
Topic: Circles: Radius, Diameter and Circumference
Category: Shapes & Geometry
File Type: PDF
File Size: 298.7 KB
Published: 13 Nov 2026
Downloads: 0

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Grade 6 math (ages 11–12) 55 minutes Geometry measurement formulas decimals problem solving

Learning Objectives

Identify and label the radius, diameter and circumference of a circle.
Use the relationship d = 2r to find the radius or diameter.
Calculate the circumference of a circle using π ≈ 3.14.

How to Use This Resource

Start with the slides: show a bicycle wheel. Ask: "How far does the bike move when the wheel turns once?"
Do the measuring investigation with round objects, then teach the formulas with the worked examples and do worksheet activities 1 and 2 together.
Students complete activities 3 to 6, then use the quiz and send the homework page home.

Classroom Activity Ideas

Pi hunt: groups measure the circumference and diameter of five round objects with string and a ruler and divide C by d.
Human circle: students stand in a circle and act as the center, a radius and a diameter.
Wheel walk: students roll a wheel once along the floor and compare the distance with C = πd.

Differentiation

Support: give circles with the radius already drawn and focus on d = 2r and C = 3 × d as an estimate. Challenge: students find the diameter when given the circumference and use the π key on a calculator.

Assessment

Use the worksheet and quiz to check circle parts and calculations. Use the rubric to assess the investigation and word problems.

Teacher Tips

Measured results will not be exactly 3.14, which is fine; the point is that C ÷ d is always a bit more than 3. Encourage students to estimate first (about 3 times the diameter) so they can spot calculation errors.

What's Included

10-page printable PDF lesson pack: teacher lesson plan with timings, materials and differentiation
Key vocabulary list (6 words with meanings and examples)
Student worksheet (6 activities)
Quiz / assessment (3 parts)
Homework practice page
Printable flashcards: 6 A5 picture cards (separate PDF)
Assessment rubric (4 levels)
Lesson slides (editable PowerPoint)
Editable Word version of all student pages
Complete answer key (also as a separate PDF)