Use our Circle Calculator to instantly compute a circle's radius, diameter, circumference, and area. Enter any one known value and get precise results with your preferred units and decimal places.
What the Circle Calculator Does
The Circle Calculator is designed to make geometry effortless. Whether you know the radius from a technical drawing, the diameter from a measurement, the circumference from a wrapped tape, or the area from a design specification, you can input any single value and the calculator derives the remaining properties. It supports common metric and imperial units, and you can choose the number of decimal places to match your reporting standards. For coursework or specific engineering conventions, you may even set a custom value for ? (pi).
Which Value Should You Enter?
- Radius (r): The distance from the center to the edge of the circle.
- Diameter (d): Twice the radius; the distance across the circle through the center.
- Circumference (C): The perimeter length around the circle.
- Area (A): The space enclosed by the circle.
Choose the value you have, enter it with the correct unit, and the calculator computes all remaining values consistently in the same unit system.
Formulas Used by the Calculator
- From radius: d = 2r, C = 2?r, A = ?r2
- From diameter: r = d/2
- From circumference: r = C/(2?)
- From area: r = ?(A/?)
Once the radius is known, all other circle properties follow directly from the standard formulas above. If you select a custom value for ?, the calculator applies it consistently across all computations.
Why Precision and Units Matter
Accuracy depends on appropriate precision and correct units. If you are estimating materials for a project, rounding to fewer decimal places may be sufficient. However, for machining, optics, or scientific applications, you might prefer higher precision. The Circle Calculator lets you control decimal places from 0 to 10, and offers units commonly used in classrooms and workshops: millimeters, centimeters, meters, inches, and feet. Area values automatically reflect squared units, such as cm2 or in2, while linear measurements remain in the selected unit.
Practical Use Cases
- DIY and Carpentry: Compute circumference to cut edge banding or trim for round tabletops.
- Engineering and Drafting: Convert a specified diameter to area for load or material calculations.
- Education: Demonstrate relationships between radius, diameter, circumference, and area with a custom ? for lesson objectives.
- 3D Printing and CNC: Validate part dimensions before manufacturing to ensure proper fit and material usage.
How to Use the Circle Calculator
- Select the known value type (radius, diameter, circumference, or area).
- Enter the numeric value and choose your unit.
- Optionally, select a custom ? and set decimal places.
- Click Calculate to see radius, diameter, circumference, and area.
It’s that simple. The tool minimizes mistakes by applying consistent formulas, units, and precision across all outputs.
Understanding Your Results
Your results will display all four circle properties. Linear measures (radius, diameter, circumference) are shown in the selected unit, while area is displayed in squared units. If you choose to show working, you’ll also see the exact steps taken, including the formulas and the value of ? used, which is especially helpful for students and educators verifying problem-solving methods.
Get Started Now
Enter any known circle value and let the Circle Calculator do the rest. With controllable precision, flexible units, and optional step-by-step working, it’s a reliable helper for study, planning, and professional tasks alike.