What is pi (π) and why is it important?

Pi is the ratio of a circle's circumference to its diameter, approximately 3.14159. It's a mathematical constant that appears in all circle calculations and many other areas of mathematics and physics.

How do I find the radius if I know the area?

Use the formula r = √(A/π). Take the area, divide by pi, then take the square root. For example, if area = 50, then r = √(50/π) ≈ √15.92 ≈ 3.99.

What's the difference between circumference and perimeter?

Circumference is the perimeter of a circle specifically. Perimeter is the general term for the distance around any closed shape. For circles, circumference and perimeter mean the same thing.

Can I use this calculator for semicircles or quarter circles?

For semicircles, calculate the full circle values and divide by 2. For quarter circles, divide by 4. Remember that the perimeter of a semicircle includes the diameter, not just half the circumference.

Circle Calculator – Area, Circumference, Radius

Calculate circle properties including area, circumference, radius, and diameter. Convert between different circle measurements with comprehensive formulas.

Circle Calculator – Area, Circumference, Radius

Calculate circle properties including area, circumference, radius, and diameter. Convert between different circle measurements with comprehensive formulas.

Calculate*

What you want to calculate

Known Value*

What measurement you know

Value*

Enter the known measurement

📐

Math visualization will appear here

Understanding Circle Calculations

Circles are fundamental geometric shapes with several important measurements. Understanding the relationships between radius, diameter, circumference, and area is essential for geometry, engineering, and many practical applications.

Circle Formulas

Key circle formulas:

Area: A = πr² (pi times radius squared)
Circumference: C = 2πr (2 times pi times radius)
Diameter: d = 2r (twice the radius)
Radius: r = d/2 (half the diameter)
Pi (π) ≈ 3.14159... (ratio of circumference to diameter)

How to Use This Calculator

Follow these simple steps to get accurate results:

Enter your calculate
Enter your known value
Enter your value
Click the "Calculate" button to see your results
Review the detailed breakdown and explanation

Why Use Our Circle Calculator – Area, Circumference, Radius?

100% free and no registration required
Instant, accurate calculations with professional formulas
Mobile-friendly design that works on any device
Privacy-focused - your data never leaves your browser
Educational content to help you understand the results

Frequently Asked Questions

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