Parts of a circle: what children learn
Year 6 pupils illustrate and name parts of circles, including the radius, diameter and circumference, and know that the diameter is twice the radius.
In this game children match descriptions and measurements to the parts of a circle. Some cards give a radius and ask for the diameter, or the other way round, so children practise doubling and halving.
This topic covers the Year 6 statutory requirement in the National Curriculum in England (Geometry – properties of shapes): pupils should be taught to “illustrate and name parts of circles, including radius, diameter and circumference and know that the diameter is twice the radius”. Year 6 pupils are usually aged 10–11.
There is no direct equivalent in the US Common Core State Standards. Radius, diameter and circumference are Grade 7 in Common Core (7.G.B.4).
How to play
Pick a card on the left, then the card on the right that matches it. Each game has 6 pairs. Wrong matches are counted as mistakes, and you get three stars for a game with no mistakes.
Step by step
- Radius. The distance from the centre to the edge.
- Diameter. A straight line from edge to edge through the centre. It is twice the radius.
- Circumference. The distance all the way round the edge.
- Double or halve. Diameter = 2 × radius. Radius = diameter ÷ 2.
Worked examples
Example 1: a straight line from edge to edge through the centre
Working: It goes right across through the middle.
Answer: diameter
Example 2: radius 7 cm
Working: Double the radius: 2 × 7 = 14.
Answer: diameter 14 cm
Example 3: diameter 30 cm
Working: Halve the diameter: 30 ÷ 2 = 15.
Answer: radius 15 cm
Common mistakes and how to fix them
- Mixing up radius and diameter. Remember the diameter goes all the way across, so it is the longer of the two.
- Drawing a 'diameter' that misses the centre. A diameter must pass through the centre.
- Thinking the circumference is a straight line. The circumference is the curved edge of the circle.
Activities to try at home
- Measure the radius and diameter of plates and lids.
- Wrap string round a tin to measure its circumference.
- Draw circles with a compass or a pin and string.
Ideas for the classroom
- Pupils fold a paper circle to find its centre and diameter.
- Measure several circular objects and compare their diameter and circumference.
- Draw circles with a compass from a given radius.
Free printable game and worksheet
The free printable starts with a game sheet, such as a colour-by-answer picture, an answer maze or a secret-code joke, followed by a worksheet. Both use the same checked questions as the online game, and the answers are on the last page. Print it, or save it as a PDF from your browser’s print menu.
Open the free printable game and worksheet
Frequently asked questions
Do children calculate circumference with π?
Not in Year 6. Using π to calculate circumference is taught at secondary school.
Why do children need to know these words?
They are used to describe circles accurately, and in Year 6 to draw circles with a compass.
Can it be played with a keyboard?
Yes. Tab to a card, press Enter to pick it, then pick its partner.