Python round() Function

The round() returns a number rounded to ndigits precision after the decimal point.

If ndigits is not specified, the number is rounded to the nearest integer.

Syntax

round(number, ndigits)

round() Parameters

Python round() function parameters:

Parameter	Condition	Description
number	Required	The number to be rounded.
ndigits	Optional	Number of decimals up to which the given number is rounded. Defaults is 0.

round() Return Value

Python round() function returns:

• nearest integer to the given number if ndigits is not provided
• number rounded off to the ndigits digits if ndigits is provided

Examples

Example 1: Basic Usage of round() function

# round integers
print(round(10))   # Output: 10

# round floating point
print(round(10.7)) # Output: 11

# round floating point (even choice behaviour)
print(round(5.5)) # Output: 6

output:

10
11
6

Example 2: Rounding to Specified Decimal Places

You can specify the number of decimal places with the ndigits parameter.

For example, let's round to 2 decimal places:

print(round(2.665, 2)) # Output: 2.67
print(round(2.675, 2)) # Output: 2.67

output:

2.67
2.67

note

When the decimal 2.675 is converted to a binary floating-point number, it's again replaced with a binary approximation, whose exact value is 2.67499999999999982236431605997495353221893310546875.

Because of this, it is rounded to 2.67 instead of 2.68.

This behaviour is common because most decimal fractions can't be represented exactly as a float. See example 4 for high-precision rounding.

Example 3: Rounding to Even (Banker's Rounding)

The round() function rounds to the nearest integer by default. However, it's important to note that round() uses "round half to even" (also known as "bankers' rounding") for rounding, which means that when a number is exactly halfway between two others, it rounds to the nearest even number.

For example:

print(round(4.4))  # Output: 4
print(round(4.5))  # Output: 4
print(round(4.6))  # Output: 5

print(round(5.4))  # Output: 5
print(round(5.5))  # Output: 6
print(round(5.6))  # Output: 6

output:

4
4
5
5
6
6

note

This behavior is standard in Python and many other programming languages.

Example 4: High-precision rounding with Decimal module and round() function

If you need precision, consider to use the decimal module, which is designed for floating-point arithmetic. For example:

from decimal import Decimal

# normal float
num = 2.675
print(round(num, 2)) # Output: 2.67

# using decimal.Decimal (passed float as string for precision)
num = Decimal('2.675')
print(round(num, 2)) # Output: 2.68

output:

2.67
2.68

note

The use of decimal module allows to avoid the possible binary approximation to represent float numbers. So, your float number will be represented correctly in memory, and so also the result of round() function will be correct.

Example 5: Round with negative ndigits parameter

The ndigits parameter can be negative.

If it is negative, it allows you to for example round numbers to ten’s or hundred’s.

For example, let's rounds to ten's:

print(round(34, -1))     # Output: 30
print(round(246, -1))    # Output: 250
print(round(456, -1))    # Output: 460

output

30
250
460

For example, let's rounds to hundred's:

print(round(34, -2))     # Output: 0
print(round(246, -2))    # Output: 200
print(round(456, -2))    # Output: 500

output

0
200
500

Example 6: