Circles – What You Need to Know for GCSE Maths

Firstly, you need to be aware of some key terminology related to circles. The diagrams below show the things you need to be able to name and recognise. Start with the circumference, which is the distance all the way around the circle. Next remember the radius (the distance from the centre to the circumference of the circle) and the diameter (the distance through the centre from one side of the circumference to the other).

Radius of a circle
The radius is the distance from the centre of the circle to the circumference.
Diameter of a circle
The diameter is the distance through the centre from one side of the circumference to the other.

Other key terms for circles

The two diagrams below show you the other key things you need to be able to name and recognise:

  • Chord – a line from one point on the circumference to another.
  • Minor Segment – smaller part of the circle created by a chord.
  • Major Segment – larger part of the circle created by a chord.
  • Tangent – a straight line outside the circle, which just touches the circumference.
  • Sector – a part of the circle created by two radii (it looks a bit like a pizza slice).
circle terms
Chord, Segment, Tangent
sector of a circle
Sector of a circle

Area and Circumference of the Circle

There are two main rules you need to know for circles. One to calculate the circumference of the a circle and one to calculate the area of a circle. Both of these are set out below (with two ways to use the circumference rule).

circumference rules

For these formulas d is the diameter r is the radius.

Area of a circle

Make sure you learn these rules and the terminology related to circles. Then have a go at our GCSE circles worksheet to practice what you have learnt. We also have related revision guides for angle facts and area and perimeter. You can contact us directly to arrange a GCSE maths lesson with one of our expert tutors.

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