⚪ Circle Calculator
Results are rounded to 4 decimal places.
What is a Circle?
A circle is a perfectly round shape in a plane, where all points on the curve are the same distance from a fixed center point. This distance is called the radius. Circles are fundamental in geometry, engineering, and everyday life.
Key Circle Terms
- Radius (r): Distance from the center to any point on the circle.
- Diameter (d): Longest distance across the circle, passing through the center. d = 2r.
- Circumference (C): Perimeter or distance around the circle.
- Area (A): Total space inside the circle.
Formulas
Circumference: C = 2 × Ï€ × r
Area: A = Ï€ × r²
If you know one property (radius, diameter, circumference, or area), you can use these formulas to find all the others. Our calculator does this instantly.
How to Use This Circle Calculator
- Select the measurement you already know (e.g., radius, diameter, circumference, or area).
- Enter the numeric value in the input field.
- The results update automatically – you’ll see the missing radius, diameter, circumference, and area calculated immediately.
- Use the Reset button to clear and start over.
Example Calculation
Suppose you have a circle with radius r = 5 units:
| Property | Formula | Result |
|---|---|---|
| Diameter | d = 2 × 5 | 10 units |
| Circumference | C = 2 × Ï€ × 5 | ≈ 31.4159 units |
| Area | A = Ï€ × 5² | ≈ 78.5398 square units |
Try it yourself using the calculator above!
Why Use an Online Circle Calculator?
- Saves time and avoids manual calculation errors.
- Great for students, teachers, engineers, and DIY projects.
- Works on any device – no installation needed.
Frequently Asked Questions
Can I enter negative numbers?
No, lengths and areas must be positive. The input only accepts non‑negative values.
Which value should I enter?
Enter the one you already have – the tool finds the rest automatically.
How accurate are the results?
We use JavaScript’s high‑precision math with Ï€ (Math.PI), and results are displayed to 4 decimal places.
