Free Circle Calculator - Area, Circumference & More
Calculate all circle properties from any measurement. Best free circle calculator 2025 - radius, diameter, area, and circumference.
Quick Answer
Circle formulas: Area = πr², Circumference = 2πr = πd, Diameter = 2r. Enter any value (radius, diameter, area, or circumference) to find all others. A circle with radius 5 has: diameter 10, area 78.54, circumference 31.42. Calculate at practicalwebtools.com.
Key Facts about Circle Calculator:
- Area = πr² (pi times radius squared)
- Circumference = 2πr = πd (pi times diameter)
- Diameter = 2 × radius
- π (pi) ≈ 3.14159265359
- Radius is distance from center to edge
- Diameter is distance across through center
- All circles are similar (same shape, different sizes)
Why Use Our Circle Calculator?
Complete circle calculations:
All Properties
Find radius, diameter, area, circumference.
Any Input
Enter any value to find all others.
Precise π
High-precision pi calculations.
Formulas Shown
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How to Circle Calculator in 3 Easy Steps
Calculate circle properties:
Enter One Value
Radius, diameter, area, or circumference.
Calculate
Find all other properties.
See Results
View all circle measurements.
Complete Circle Analysis
Find all properties from any one measurement
High-precision calculations
See formulas used
Perfect for math and practical applications
Common Use Cases for Circle Calculator
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Frequently Asked Questions
Everything you need to know about our circle calculator
How do I calculate circle area?
Area = πr². Radius 5: π × 25 = 78.54.
Area = πr² (pi times radius squared). For radius 5: Area = π × 25 = 78.54. If you have diameter, first divide by 2 to get radius.
How do I find circumference?
C = 2πr or πd. Radius 5: 2π × 5 = 31.42.
Circumference = 2πr or πd (pi times diameter). For radius 5: C = 2 × π × 5 = 31.42. For diameter 10: C = π × 10 = 31.42.
What is the difference between radius and diameter?
Radius: center to edge. Diameter: across center. d = 2r.
Radius is the distance from center to edge. Diameter is the distance across through the center. Diameter = 2 × radius.
What is pi (π)?
Ratio of circumference to diameter ≈ 3.14159.
Pi is the ratio of circumference to diameter, approximately 3.14159. It is irrational (infinite non-repeating decimal) and appears in all circle calculations.
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