Math.PI

Added in vES1 · Updated March 14, 2026 · Math

javascript math constants pi geometry

Math.PI is a static property of the Math object that represents the ratio of a circle’s circumference to its diameter — approximately 3.141592653589793. It is a read-only constant; you cannot change its value.

Syntax

Math.PI

Value

Math.PI; // 3.141592653589793

This constant is the same as the mathematical constant π (pi) and is used extensively in geometric calculations involving circles, spheres, and trigonometric functions. Unlike functions like Math.sin() or Math.cos() which require you to know trigonometric concepts, Math.PI is simply a useful shortcut for the ubiquitous π value.

Examples

Basic Usage

console.log(Math.PI);
// 3.141592653589793

Calculating Circle Circumference

The circumference of a circle is calculated using the formula C = 2πr:

function circumference(radius) {
  return 2 * Math.PI * radius;
}

console.log(circumference(5));
// 31.41592653589793

console.log(circumference(10));
// 62.83185307179586

console.log(circumference(1));
// 6.283185307179586

Calculating Circle Area

The area of a circle is calculated using the formula A = πr²:

function circleArea(radius) {
  return Math.PI * radius * radius;
}

console.log(circleArea(5));
// 78.53981633974483

console.log(circleArea(7));
// 153.93804002589985

console.log(circleArea(0));
// 0

Calculating Sphere Volume

The volume of a sphere uses the formula V = (4/3)πr³:

function sphereVolume(radius) {
  return (4/3) * Math.PI * Math.pow(radius, 3);
}

console.log(sphereVolume(1));
// 4.188790204786391

console.log(sphereVolume(2));
// 33.51032163819093

console.log(sphereVolume(10));
// 4188.790204786391

Converting Degrees to Radians

Degrees and radians are two ways to measure angles. To convert degrees to radians:

function degreesToRadians(degrees) {
  return degrees * (Math.PI / 180);
}

console.log(degreesToRadians(90));
// 1.5707963267948966

console.log(degreesToRadians(180));
// 3.141592653589793

console.log(degreesToRadians(360));
// 6.283185307179586

Converting Radians to Degrees

To convert radians back to degrees:

function radiansToDegrees(radians) {
  return radians * (180 / Math.PI);
}

console.log(radiansToDegrees(Math.PI));
// 180

console.log(radiansToDegrees(Math.PI / 2));
// 90

console.log(radiansToDegrees(0));
// 0

Common Patterns

Drawing a Circle in Canvas

When drawing circles on an HTML5 canvas, Math.PI is essential:

function drawCircle(ctx, x, y, radius) {
  ctx.beginPath();
  ctx.arc(x, y, radius, 0, 2 * Math.PI);
  ctx.stroke();
}

// Draws a circle at (100, 100) with radius 50
drawCircle(ctx, 100, 100, 50);

The ctx.arc() method takes start and end angles in radians, so 2 * Math.PI represents a full circle from 0 to 360 degrees.

Calculating Angles with Trigonometry

While we don’t have dedicated sin() and cos() pages, JavaScript does provide these functions. Math.PI is essential when using them:

// Full rotation (360 degrees)
const fullRotation = 2 * Math.PI;

// Quarter rotation (90 degrees)
const quarterRotation = Math.PI / 2;

// Half rotation (180 degrees)
const halfRotation = Math.PI;

Creating Circular Animations

function getCirclePoint(centerX, centerY, radius, angleInDegrees) {
  const radians = angleInDegrees * (Math.PI / 180);
  return {
    x: centerX + radius * Math.cos(radians),
    y: centerY + radius * Math.sin(radians)
  };
}

// Get point on circle at 45 degrees
const point = getCirclePoint(100, 100, 50, 45);
console.log(point);
// { x: 135.3553390593274, y: 135.3553390593274 }

Why Use Math.PI?

Using Math.PI instead of manually typing 3.14159... provides several advantages:

Precision — The constant is defined to full floating-point precision
Readability — Code is clearer when you use Math.PI instead of magic numbers
Consistency — Calculations are guaranteed to use the same value everywhere
Performance — The value is computed once by the JavaScript engine