How to Use Math.sqrt in JavaScript: Simple Square Root Calculation

Use Math.sqrt(x) in JavaScript to find the square root of a number x. It returns the positive square root or NaN if x is negative.

Syntax

The Math.sqrt() function takes one argument, a number, and returns its square root. If the number is negative, it returns NaN (Not a Number).

• Math.sqrt(x): x is the number you want the square root of.

javascript

Math.sqrt(x)

Example

This example shows how to calculate the square root of 16 and 25 using Math.sqrt(). It also shows what happens if you try to find the square root of a negative number.

javascript

console.log(Math.sqrt(16));  // 4
console.log(Math.sqrt(25));  // 5
console.log(Math.sqrt(-9));  // NaN

Output

4
5
NaN

Common Pitfalls

Common mistakes include passing negative numbers, which results in NaN, and passing non-numeric values, which can cause unexpected results.

Always ensure the input is a non-negative number to get a valid square root.

javascript

console.log(Math.sqrt(-4));  // NaN (wrong if expecting a real number)

// Correct approach: check before calling
const num = -4;
if (num >= 0) {
  console.log(Math.sqrt(num));
} else {
  console.log('Cannot calculate square root of negative number');
}

Output

NaN
Cannot calculate square root of negative number

Quick Reference

Usage	Description
Math.sqrt(x)	Returns the square root of x
x >= 0	Input must be zero or positive for a real result
Negative input	Returns NaN (Not a Number)
Non-numeric input	Returns NaN or converts if possible

Key Takeaways

Use Math.sqrt(x) to get the square root of a non-negative number x.

Passing a negative number to Math.sqrt returns NaN, not a real number.

Always check that the input is zero or positive before using Math.sqrt.

Math.sqrt only accepts one argument, the number to find the root of.

Non-numeric inputs may cause unexpected results or NaN.