Circle Calculator — Instantly Find Diameter, Circumference & Area

A circle calculator is a tool used to compute key properties of a circle—such as diameter, circumference, and area—based on a single known input: the radius.

Whether you're a student, teacher, engineer, or DIY enthusiast, this calculator can help you quickly solve circle-related geometry problems without doing the math by hand.

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What This Calculator Does

Using just the radius, it instantly calculates:

• Diameter: Distance across the circle through the center
• Circumference: The total distance around the circle
• Area: The space inside the circle

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How to Use the Circle Calculator

Step 1:
Enter the radius of the circle in the input box.
Example: 10 (for a 10 cm radius)

Step 2:
Click the “Calculate” button.

Step 3:
Your results will appear below, showing:

• Diameter (2 × radius)
• Circumference (2 × π × radius)
• Area (π × radius²)

All outputs are shown in centimeters and square centimeters.

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Why Use a Circle Calculator?

Manual calculations can be tedious and prone to error. With this calculator, you:

• Save time
• Reduce mistakes
• Work faster on assignments or projects
• Get consistent results using the mathematical constant π ≈ 3.14159

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FAQ: Circle Calculator

Q1: What is the formula for the diameter of a circle?
A1: Diameter = 2 × radius

Q2: How do you calculate circumference?
A2: Circumference = 2 × π × radius

Q3: What is the formula for the area of a circle?
A3: Area = π × radius²

Q4: Can I enter the diameter instead of the radius?
A4: This calculator currently accepts radius only, but you can manually divide your diameter by 2 first.

Q5: What unit is used?
A5: All inputs and outputs are in centimeters (cm) and square centimeters (cm²).

Q6: Can I use this for real-world tasks like cutting circles in materials?
A6: Yes, as long as your radius input matches your real-world measurement unit, the results will be accurate.