How circle area is calculated
The area of a circle is pi times the radius squared. Pi (π) is a constant, approximately 3.14159, representing the ratio of a circle's circumference to its diameter.
area = π × radius²
Converting between radius, diameter and circumference
If you know the diameter instead of the radius, just divide by 2. If you only know the circumference, divide by 2π to recover the radius, then use the area formula as usual.
radius = diameter ÷ 2
radius = circumference ÷ (2 × π)
circumference = 2 × π × radius
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Common uses
- Home projects: figuring out how much material covers a round table, rug, or pool.
- Landscaping: estimating soil or mulch needed for a circular garden bed.
- School and homework: quick geometry checks for circle problems.
Frequently asked questions
What's the difference between circumference and perimeter?
They mean the same thing for a circle — "circumference" is simply the specific term used for the perimeter (the distance around the outside) of a circle.
Does the unit matter?
No specific unit is assumed — enter your measurement in whatever unit you're working with (cm, inches, meters), and the area will be in that same unit squared.