# Circle Formula Calculator

Created by Luis Hoyos
Reviewed by Wojciech Sas, PhD candidate
Last updated: Mar 15, 2022

The circle formula calculator allows you to make circle calculations easily. Keep reading to learn things like:

• What is the formula to calculate the diameter of a circle given its radius, or vice versa.
• What is the formula for calculating the circumference of a circle.
• What is the formula for the area of a circle.

## Circle formulas

Although using the circle formula calculator is the fastest way to make circle calculations, it's crucial to know the formulas to understand the process better.

### Formula to calculate the diameter of a circle given its radius, or vice versa

The formula of the diameter of a circle is the most straightforward of the equations and says that diameter (d) equals twice the radius (r):

d = 2r
r = d/2

The calculation of circumference and area of a circle formulas are more tricky. Look at the equations in the following sections.

### Formula to calculate the circumference of a circle

The formula of the circle circumference (c) can be expressed in terms of radius, diameter, and area (A), as shown below:

c = 2πr
c = πd
c = 2√(πA)

### Formula to calculate the area of a circle

We can express the formula to calculate the area of a circle in terms of the radius, diameter, and circumference:

A = πr²
A = πd²/4
A = c²/(4π)

## How to use the area and circumference of a circle formula? An example

Suppose you have a circle of radius 3 cm. If you want to calculate its area and circumference, you can do it following these steps:

1. Input the radius in the circle area formula:
A = π × (3 cm)² = 28.2743 cm².
2. Also, input the radius in the circumference formula:
c = 2π × (3 cm) = 18.8496 cm.
3. Check your results with the circle formula calculator. The results should also be 28.2743 cm² and 18.8496 cm for area and circumference.

## Other helpful tools like the circle formula calculator

Now that you know how to calculate the formula of circumference and area of a circle take a look 👀 at other calculators:

## FAQ

### What is the formula for the perimeter of a half-circle?

π (pi) times radius phalf = πr. The formula for the perimeter of a half-circle is the same formula for the circle circumference, divided by two. That results in the product of π (pi) and the radius.

### What is the radius of a 3.65-inch diameter circle?

1.825 in. The formula for the diameter of a circle says diameter is twice the radius. To find the radius, simply divide the diameter by two: r = 3.65 in / 2 = 1.825 in.

Luis Hoyos in
Diameter (d)
in
Circumference (c)
in
Area (A)
in²
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