Circle Calculator
Calculate the parts of a circle using radius, diameter, or circumference for design, schoolwork, and DIY projects.
Perimeter (Circumference)
31.41593
Area
78.53982
Circle Calculations ◯
Calculate area and circumference using either radius or diameter, or calculate area and radius/diameter using circumference.
Key Facts
- Radius or diameter is required to calculate area and circumference.
- Circumference can be used to calculate radius, diameter and area.
Formulas
- Area (from radius)
Area = π × r²- r is the radius of the circle. Area represents the space enclosed within the circle. If you know the circumference, you can first calculate r = C ÷ (2 × π). - Circumference (from radius)
Circumference = 2 × π × r- r is the radius. Circumference is the distance around the circle. Cannot derive radius/diameter from circumference alone without calculation. - Radius (from circumference)
r = Circumference ÷ (2 × π)- You can calculate radius if you know the circumference. Once r is known, area can be calculated.
Example Calculations 🔢
- Radius = 5, Diameter = 10, Circumference ≈ 31.42, Area ≈ 78.54
- Circumference = 53, Radius ≈ 8.44, Area ≈ 223.53
FAQs
Can I calculate diameter from circumference?
Yes, diameter = circumference ÷ π. You can also calculate radius = circumference ÷ (2 × π).
What inputs are allowed?
You can enter either radius, diameter, or circumference depending on the mode. Results are computed based on what is mathematically derivable from the input.