Circle Calculator
Calculate circle area, circumference, and diameter from any known measurement — radius, diameter, circumference, or area — with unit conversion support.
Circle Geometry Calculator
Enter any one measurement to calculate all circle properties
Key Features
Understanding Circle Formulas
Circle Calculation Tips
Common Use Cases
How to Use the Circle Calculator
Step-by-Step Instructions
- 1Choose what measurement you know: radius, diameter, circumference, or area
- 2Enter the known value in the input field
- 3Select the appropriate unit (cm, m, in, ft)
- 4View all calculated circle properties instantly
- 5Copy results or clear all to start over
Example Calculations
- Radius 5 cm: Diameter = 10 cm, Area = 78.54 cm², Circumference = 31.42 cm
- Diameter 20 in: Radius = 10 in, Area = 314.16 in², Circumference = 62.83 in
- Circumference 31.42 ft: Radius = 5 ft, Diameter = 10 ft, Area = 78.54 ft²
Frequently Asked Questions
What is the value of π (pi) used in calculations?
Our calculator uses π ≈ 3.141592653589793 for maximum precision. This ensures accurate results for all circle calculations including area and circumference.
How do I convert between different units?
Simply select your desired unit from the dropdown menu. The calculator will display results in the same unit you choose for input. For conversions between units, use our conversion tools or multiply by appropriate conversion factors.
Can I calculate a circle from its area?
Yes! Our calculator now accepts area as an input option. Simply select "Area (A)" from the dropdown menu and enter the area value. The calculator will automatically calculate the radius using r = √(A/π) and then determine all other circle properties.
Why is my circumference result not a whole number?
Circle circumferences involve π (pi), which is an irrational number with infinite decimal places. This means circumference calculations typically result in decimal numbers, which is mathematically correct.
How accurate are the calculations?
Our calculator provides results accurate to many decimal places using the precise value of π. For practical applications, you can round results to the number of decimal places needed for your specific use case.
What's the difference between circumference and perimeter?
For circles, circumference and perimeter mean the same thing - the distance around the outside of the circle. The term "circumference" is specifically used for circles, while "perimeter" is the general term for any shape.
Why Choose Our Circle Calculator?
Step-by-Step Instructions
Choose Your Input Method
Select whether you want to calculate using radius, diameter, circumference, or area as your starting point.
Enter Your Value
Input the known measurement in the corresponding field. Use decimal numbers for precision when needed.
Select Units
Choose your measurement units (inches, centimeters, meters, etc.) for accurate calculations and results.
Calculate Results
Click "Calculate" to instantly compute all circle properties including area, circumference, radius, and diameter.
Review Visual Display
Examine the visual circle diagram that shows your input and all calculated measurements for verification.
Copy or Save Results
Use the copy buttons to save individual measurements or export all results for your project documentation.
Pro Tips
Accurate Measurements: Use the most precise measurement you have available. More decimal places in input yield more accurate results.
Cross-Check Values: Verify your input by checking if the calculated values make sense relative to each other and your expectations.
Unit Consistency: Always ensure your units are consistent throughout your project. The calculator handles conversions automatically.
Real-World Applications: Perfect for construction, engineering, crafts, gardening, or any project involving circular measurements.
Educational Use: Great for students learning geometry concepts and seeing how circle formulas work in practice.
Related Calculators
Abacus
Online abacus calculator
Basic Calculator
Simple arithmetic calculator
Number Base Converter
Convert between number bases
Area Converter
Convert area measurements
Home Affordability Calculator
Calculate home buying budget
Age Calculator
Calculate exact age and life statistics