# Write a Program in JavaScript to Find Area of Circle | Area of Circle in JavaScript

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Write a program in __javascript__ to find area of circle.

In this article, you will learn how to write a program in javascript to find area of circle.

### Formula

*D = 2 * r*

*C = 2 * PI * r*

*A = PI * r ^{2}*

### Where

**R = radius of the circle**

**D = diameter of the circle**

**C = circumference of the circle**

**A = area of the circle**

There are two ways to implement these formulae:

- By using the default value of PI =
**3.14** - Second, by using
**Math.PI**constant

## 1. By using the default value of PI = 3.14

```
/* Write a Program in JavaScript to Find Area of Circle | Area of Circle in JavaScript */
<script type="text/javascript">
var r, d, c, a;
// r = radius
// d = diameter
// c = circumference
// a = area
/* Calculation of diameter, circumference, and area */
r = 10;
d = 2 * 10;
c = 2 * 3.14 * 10;
a = 3.14 * (10 * 10);
document.write("Diameter = " + d + " units<br />");
document.write("Circumference = " + c + " units<br />");
document.write("Area = " + a + " sq. units");
</script>
```

### Output

`Diameter = 20 units`

Circumference = 62.800000000000004 units

Area = 314 sq. units

## 2. By using **Math.PI** constant

```
/* Write a Program in JavaScript to Find Area of Circle | Area of Circle in JavaScript */
<script type="text/javascript">
var r, d, c, a;
// r = radius
// d = diameter
// c = circumference
// a = area
/* Calculation of diameter, circumference, and area */
r = 10;
d = 2 * 10;
c = 2 * Math.PI * 10;
a = Math.PI * (10 * 10);
document.write("Diameter = " + d + " units<br />");
document.write("Circumference = " + c + " units<br />");
document.write("Area = " + a + " sq. units");
</script>
```

### Output

`Diameter = 20 units`

Circumference = 62.83185307179586 units

Area = 314.1592653589793 sq. units