Circle Formulas
2D Shapes
Circle
- Area
- A = πr2
- Circumference
- C = 2πr
- Diameter
- d = 2r
- r radius
- d diameter
- π ≈ 3.14159
Circle formulas explained
Every point on a circle is the same distance r from the centre. π (pi) ≈ 3.14159 links the radius to the circumference and area. Below are all the circle formulas with what each letter means, a worked example and a free calculator.
- Area:
A = πr² - Circumference:
C = 2πr - Diameter:
d = 2r
Circle calculator
Live calculator
Circle calculator
Worked example: area of a circle
Given Radius r = 5 cm, substitute the values into each circle formula:
- A = π × 5² = 78.54 cm²
- C = 2 × π × 5 = 31.42 cm
- d = 2 × 5 = 10 cm
Circle Formula SheetFormulas, variables, a worked example and practice questions with answers.Download PDFOpen
Circle formulas FAQ
What is the formula for the area of a circle?
The area of a circle is A = πr², where r is the radius, π ≈ 3.14159.
What is the formula for the circumference of a circle?
The circumference of a circle is C = 2πr, where r is the radius, π ≈ 3.14159.
What is the formula for the diameter of a circle?
The diameter of a circle is d = 2r, where r is the radius, d is the diameter.
Can I download the circle formulas as a PDF?
Yes. Use the Download PDF button on this page for a free printable circle formula sheet with a worked example and practice questions.
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