This key facts covers The Two Essential Formulas within Circumference & Area of Circles for GCSE Mathematics. Revise Circumference & Area of Circles in Geometry & Measures for GCSE Mathematics with 11 exam-style questions and 7 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 3 of 10 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
The Two Essential Formulas
Circumference
C = πd
or C = 2πr
Area
A = πr²
pi × radius × radius
⚠️ Area uses radius SQUARED! This is the most common mistake.
Practice questions for Circumference & Area of Circles
A circle has radius r. Which pair of formulas gives the correct circumference C and area A?
Explain why the circumference of a circle is measured in cm (or other length units) but the area is measured in cm² (square units).