# Circle Formula Calculator

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

- 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`

):

`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 by following these steps:

- Input the radius in the circle area formula:

`A = π × (3 cm)² = 28.2743 cm²`

. - Also, input the radius in the circumference formula:

`c = 2π × (3 cm) = 18.8496 cm`

. **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:

- Circle calc: find c, d, a, r;
- Circle measurements calculator;
- Circumference to diameter calculator;
- Radius of a circle calculator;
- Circle length calculator;
- Circumference and area of a circle calculator;
- Diameter of a circle calculator;
- Circle perimeter calculator;
- Square footage of a circle calculator; and
- Square inches of a circle calculator.

## FAQ

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

π (pi) times radius p_{half} = 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 the diameter is twice the radius. To find the radius, simply divide the diameter by two: `r = 3.65 in / 2 = 1.825 in`

.