Circle Calculator
Calculate circle properties including radius, diameter, circumference, and area. Enter any one known value to compute all circle dimensions instantly. Free online circle calculator with formulas and visual chart.
About This Calculator
About the Circle Calculator
This calculator computes all key properties of a circle -- radius, diameter, circumference, and area -- from any single known value. Whether you know the radius, diameter, circumference, or area, simply select the input type and enter the value to get instant results for all four properties.
Key Formulas
- Diameter: d = 2r
- Circumference: C = 2pir
- Area: A = pir^2
Where r is the radius and pi (pi) is approximately 3.14159. If you know the diameter, circumference, or area instead, the calculator first derives the radius from your input using the inverse formulas, then computes all other properties.
How to Use
- Select the Known Value type from the dropdown -- Radius, Diameter, Circumference, or Area.
- Enter the numeric value in the input field.
- Click Calculate to see all four circle properties displayed instantly.
The result card shows the radius, diameter, circumference, and area alongside a pie chart and bar chart comparing the computed values across all four dimensions.
Applications
Circle calculations are essential in geometry, engineering, architecture, construction, manufacturing, landscaping, and everyday problem-solving -- from determining material needed for a circular table to designing wheels, pipes, and storage tanks.
Frequently Asked Questions
How do you calculate circle properties from the radius?
Given the radius r: diameter = 2r, circumference = 2pir, and area = pir^2. Select Radius from the dropdown, enter the value, and all properties are computed instantly.
How do I find the radius from the circumference?
The radius can be found from the circumference using r = C / (2pi). Select Circumference from the dropdown, enter the circumference value, and the calculator will compute the radius and all other properties.
What is the relationship between diameter and radius?
The diameter is twice the radius (d = 2r). Conversely, the radius is half the diameter (r = d/2). If you enter the diameter, the calculator automatically divides by 2 to get the radius before computing other properties.
How do I calculate the area of a circle from the diameter?
The formula for area using diameter is A = pid^2/4, where d is the diameter. The calculator handles this conversion automatically -- select Diameter as input, enter the value, and the area is computed from the radius derived from the diameter.
Why is the circumference formula 2pir?
pi (pi) is the ratio of a circle's circumference to its diameter (approximately 3.14159). Since the diameter is 2r, the circumference C = pi x d = pi x 2r = 2pir. This relationship holds for every circle.
What units does this circle calculator support?
The calculator works with any consistent unit system. Enter length in any unit (cm, m, inches, feet) and the results will be in the same unit for linear measurements and the corresponding square unit for area.
Is this circle calculator free to use?
Yes, this circle properties calculator is completely free to use with no registration, limits, or subscription required.