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Diameter - GCSE Maths Definition

Reviewed by: Naomi C

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What is a diameter?

In GCSE Maths, a diameter is a line that goes through the centre of a circle and whose ends touch the circumference at two different points. A diameter is a line of symmetry of a circle, as it cuts a circle exactly into two halves. 

A circle with a straight line crossing through the centre from one point on the circumference to another point on the circumference. The line is labelled “diameter”.
A circle showing a diameter

It is useful to remember that a diameter is twice the length of a radius for a circle. The diameter can be used to calculate the area or circumference of a circle, as well as having other applications in areas such as circle theorems.

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Naomi C

Reviewer: Naomi C

Expertise: Maths Content Creator

Naomi graduated from Durham University in 2007 with a Masters degree in Civil Engineering. She has taught Mathematics in the UK, Malaysia and Switzerland covering GCSE, IGCSE, A-Level and IB. She particularly enjoys applying Mathematics to real life and endeavours to bring creativity to the content she creates.

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