`math.sqrt()` Function Explained

math.sqrt() returns the square root of a number in Python. It is part of the math module, so you need to import that module before using it.

This function is useful when writing formulas, solving geometry problems, or doing basic calculations. On this page, you will learn what math.sqrt() does, what it returns, when to use it, and the most common beginner mistakes.

Quick answer

import math

result = math.sqrt(25)
print(result)  # 5.0

Use math.sqrt() after importing the math module. It returns a float.

What `math.sqrt()` does

Returns the square root of a number
Comes from Python’s built-in math module
You must write import math before using it
The result is usually returned as a float

A square root is a number that multiplies by itself to make the original number.

For example:

The square root of 9 is 3
The square root of 25 is 5

If you are new to the math module, see the Python math module overview.

Basic syntax

The syntax is:

math.sqrt(x)

Here:

x should be a number
x is usually an int or float
The function returns the square root of x

Example:

import math

print(math.sqrt(9))

Output:

3.0

Simple working example

Here is a complete example:

import math

number = 36
result = math.sqrt(number)

print(result)

Output:

6.0

What this code does:

Imports the math module
Stores 36 in the variable number
Calculates the square root with math.sqrt(number)
Prints the result

What the return value looks like

math.sqrt() returns a float.

That means even if the answer looks like a whole number, Python usually shows it with .0.

Example:

import math

print(math.sqrt(16))

Output:

4.0

This is normal. The function returns 4.0, not 4.

If you need to understand floats better, see Python float() explained and Python numbers explained: int, float, complex.

Only convert the result to an integer if you are sure the square root should be a whole number.

import math

result = math.sqrt(16)
print(int(result))

Output:

When to use `math.sqrt()`

Use math.sqrt() when:

You want the square root of a positive number
You are writing math formulas
You are working with distance, geometry, or basic calculations

Example:

import math

side = 49
length = math.sqrt(side)

print(length)

This is clearer than writing a more complex expression when all you need is a square root.

Negative numbers and errors

math.sqrt() does not support negative numbers in normal real-number math.

Example:

import math

print(math.sqrt(-1))

This raises:

ValueError: math domain error

Why this happens:

math.sqrt() works with real numbers
The square root of a negative number is not a real number
So Python raises an error instead of returning a result

If this is the error you are seeing, read how to fix ValueError: math domain error.

A simple way to avoid this problem is to check the value first:

import math

value = 25

if value >= 0:
    print(math.sqrt(value))
else:
    print("Cannot take the square root of a negative number")

Common beginner mistakes

Here are the most common problems when using math.sqrt().

Forgetting to import `math`

This causes an error because Python does not know what math is.

Wrong:

result = math.sqrt(25)
print(result)

Right:

import math

result = math.sqrt(25)
print(result)

Writing `sqrt(9)` instead of `math.sqrt(9)`

If you only write sqrt(9), Python will usually raise a NameError.

Wrong:

import math

print(sqrt(9))

Right:

import math

print(math.sqrt(9))

Passing a string instead of a number

This will fail because "25" is text, not a number.

Wrong:

import math

print(math.sqrt("25"))

You can check the type of a value with:

value = "25"
print(type(value))
print(value)

Right:

import math

value = "25"
number = float(value)

print(math.sqrt(number))

Using a negative value without checking first

If the value might be negative, test it before calling math.sqrt().

import math

value = -9

if value >= 0:
    print(math.sqrt(value))
else:
    print("Value must be 0 or greater")

Expecting an integer but getting a float

This is normal behavior.

import math

print(math.sqrt(25))

Output:

5.0

Alternatives to `math.sqrt()`

You can also calculate a square root with x ** 0.5.

Example:

x = 25
print(x ** 0.5)

Output:

5.0

This works, but math.sqrt(x) is often easier for beginners to read. It clearly shows that you want the square root.

FAQ

Do I need to import `math` to use `sqrt()`?

Yes. Use import math, then call math.sqrt(number).

Why does `math.sqrt(9)` return `3.0` instead of `3`?

Because math.sqrt() returns a float.

Can `math.sqrt()` work with negative numbers?

Not in the regular math module for real numbers. It raises ValueError.

Is `math.sqrt()` better than `x ** 0.5`?

For beginners, math.sqrt() is often clearer and easier to read.

math.sqrt() Function Explained

`math.sqrt()` Function Explained