How to Use round() Function in Python: Syntax and Examples

Use the round() function in Python to round a number to a specified number of decimal places. The syntax is round(number, digits), where digits is optional and defaults to 0, rounding to the nearest integer.

Syntax

The round() function takes two arguments:

• number: The number you want to round.
• digits (optional): The number of decimal places to round to. If omitted, it rounds to the nearest integer.

python

round(number, ndigits=0)

Example

This example shows how to round numbers to different decimal places using round().

python

print(round(3.14159))        # Rounds to nearest integer
print(round(3.14159, 2))     # Rounds to 2 decimal places
print(round(3.14159, 3))     # Rounds to 3 decimal places
print(round(123.456, -1))    # Rounds to nearest 10

Output

3
3.14
3.142
120.0

Common Pitfalls

Be careful with floating-point rounding errors because some decimal numbers can't be represented exactly in binary. Also, when rounding halfway values (like 2.5), Python rounds to the nearest even number (called bankers rounding).

Example of unexpected rounding:

python

print(round(2.5))  # Outputs 2, not 3
print(round(3.5))  # Outputs 4

Output

2
4

Quick Reference

Usage	Description
round(number)	Rounds to nearest integer
round(number, digits)	Rounds to specified decimal places
round(number, negative_digits)	Rounds to left of decimal (e.g., -1 rounds to nearest 10)

Key Takeaways

Use round(number, digits) to round numbers to a specific decimal place.

If digits is omitted, round() returns an integer.

Python uses bankers rounding for .5 values, rounding to the nearest even number.

Floating-point numbers may show small rounding errors due to binary representation.

Negative digits round to positions left of the decimal point.