Geometry
Circle area & circumference
- where
- area (m²)
- diameter (m)
- circumference (m)
Explain this equation
Finds the area and circumference of a circle from its diameter. Use it for round tables, circular openings, column bases or the edging around a curved feature.
d is the diameter, the full width across the centre, in metres. A is the area enclosed in m². C is the distance round the edge in metres. π is the fixed ratio of a circle's circumference to its diameter, about 3.1416.
The usual area formula is πr². Because the radius is half the diameter, r² = d²/4, giving A = πd²/4. The circumference is π times the diameter by definition.
A 2 m circle is about 3.14 m² with a circumference of about 6.28 m. Doubling d doubles C but makes A four times larger.
Watch out: decide whether you mean the inside, outside or centreline diameter. On a ring of edging the difference can be significant.
Calculate a circular feature from its diameter.
Enter your values to see the result.
Good to know
Use the correct setting-out line: inside, outside or centreline.
Sources
- Geometry / arithmetic
This is a calculation aid, not a structural design or compliance certificate. Every default is an example, not a specification for your project.