Circle Measurements
Compute diameter, circumference, and area from any circle's radius. Free circle calculator with A = pir^2, C = 2pir formulas, chart, and step-by-step results.
About This Calculator
The Circle Measurements Calculator computes the diameter, circumference, and area of any circle from its radius. This tool is useful for students learning geometry, professionals in engineering and construction, and DIY enthusiasts measuring circular objects. Simply enter the radius in any unit and get all three key circle measurements instantly with a chart visualization.
Three core formulas are used: diameter D = 2r, circumference C = 2pir, and area A = pir^2. The calculator uses the mathematical constant pi (pi) approximated to high precision. The results panel displays all three values and offers a chart comparing the proportion of radius to diameter, and a comparison chart of all computed dimensions.
How to Use
Enter the radius of your circle in the input field (in any unit such as cm, m, inches, or feet) and click Calculate. The calculator instantly outputs the diameter, circumference, and area. Use the chart toggles to visualize the proportional relationship between the dimensions.
Frequently Asked Questions
How do you calculate the diameter of a circle from the radius?
The diameter is calculated by doubling the radius: D = 2r. If the radius is 5 units, the diameter is 10 units. This calculator computes diameter, circumference, and area simultaneously from a single radius input.
What is the formula for circumference of a circle?
The circumference of a circle is given by C = 2pir, where r is the radius. Alternatively, using the diameter d, C = pid. For a circle with radius 10, the circumference is approximately 62.83 units.
How is the area of a circle calculated?
The area of a circle is calculated using A = pir^2, where r is the radius. If the radius is 7 units, the area is approximately 153.94 square units. The calculator uses JavaScript's built-in Math.PI constant for high-precision results.
What units does the circle measurements calculator support?
The calculator works with any consistent unit system. If you enter the radius in meters, the diameter and circumference will be in meters and the area in square meters. Use inches, feet, centimeters -- any unit works as long as it is used consistently.
Is the circle measurements calculator free to use?
Yes, all calculators on Calculy are completely free to use with no registration, limits, or hidden fees.
Can I bookmark or share my calculation results?
Yes. After entering a radius and calculating, the value is saved in the page URL. You can copy the URL to bookmark the calculation or share it with others.