Circle Geometry Basics for 11+ Maths
21 October 2026
Understanding circles
A circle is a perfectly round shape where every point on the edge is the same distance from the centre. This fixed distance is called the radius.
Key terms to know
Centre: The exact middle point of the circle.
Radius: The distance from the centre to any point on the circle.
Diameter: A straight line passing through the centre, touching two points on the edge. The diameter is always twice the radius.
Chord: A straight line joining two points on the circle, but not always passing through the centre.
Arc: A part of the edge (circumference) of the circle between two points.
Circumference: The total distance all the way around the circle.
Why circle geometry matters for 11+
Understanding the properties of circles helps children solve questions about shapes, measurement and reasoning. These basics are often tested in 11+ Maths exams.
Key insight: The diameter is always twice the radius
If you know the radius, you can quickly find the diameter by multiplying by 2. This relationship is used in many exam questions.
Worked example
Finding the circumference of a circle with radius 7 cm
Step 1: Recall the formula. Circumference = 2 × π × radius.
Step 2: Substitute the radius. Circumference = 2 × π × 7 cm.
Step 3: Multiply the numbers. 2 × 7 = 14, so Circumference = 14 × π cm.
Step 4: Use π ≈ 3.14 for a simple calculation. 14 × 3.14 = 43.96 cm.
The correct answer is 43.96 cm.
Supporting your child
Encourage your child to draw circles and label the centre, radius, diameter, chord and arc. Practising these terms helps make geometry less intimidating.
Further practice
For more resources and worksheets on circles, visit our 11+ Maths: Circles page and try out the circle geometry practice materials.
