How to Round Numbers in Python

Decimal values are common in Python programs, especially when working with calculations, measurements, percentages, prices, and statistical data. Sometimes a calculation produces more decimal digits than you actually need, making the result difficult to read or present.

Python provides a built-in function called round() that can reduce the number of decimal places in a numeric value. You can use it to round a number to a specific precision or, when no precision is supplied, obtain a rounded integer value.

What is the round() Function in Python?

The round() function takes a number and optionally a number of decimal places. It returns the rounded result.

Syntax

round(number, ndigits)

Here:

number: The value you want to round.
ndigits: The number of digits to keep after the decimal point. This argument is optional.

If ndigits is omitted, Python rounds the value to the nearest integer.

Rounding a Number to the Nearest Integer

The simplest use of round() is to provide only the number. Python then returns a rounded integer value.

print(round(15))
print(round(25.8))
print(round(25.4))

Output

15
26
25

In this example, 25.8 is closer to 26, while 25.4 is closer to 25.

Round a Number to Specific Decimal Places

When you need a particular number of digits after the decimal point, pass the desired precision as the second argument.

print(round(25.4654, 2))
print(round(25.4276, 3))
print(round(25.4173, 2))

Output

25.47
25.428
25.42

The second argument tells Python how many decimal places should be considered in the rounded result.

Rounding the Result of a Calculation

Rounding is particularly useful when a mathematical operation produces a long decimal value. For example, dividing 1 by 6 produces several digits after the decimal point.

value = 1 / 6

print(value)
print(round(value, 2))

Output

0.16666666666666666
0.17

The original calculation produces a long floating-point representation, while round(value, 2) reduces it to two decimal places.

How Does Python Round Halfway Values?

One important detail about Python’s round() function is its treatment of values that fall exactly halfway between two possible rounded numbers.

Python uses a rule commonly called round half to even, also known as banker’s rounding. Instead of always rounding a halfway value upward, Python chooses the nearest even value.

print(round(5.5))
print(round(6.5))

Output

6
6

Both results are 6. The value 5.5 is between 5 and 6, so it becomes the even number 6. Similarly, 6.5 lies between 6 and 7, and Python selects 6 because it is the even choice.

This behavior is intentional and is part of Python’s rounding rules.

Round a Number to One Decimal Place

To keep only one digit after the decimal point, pass 1 as the second argument.

price = 19.678

result = round(price, 1)

print(result)

Output

19.7

Round a Number to Two Decimal Places

Two decimal places are frequently useful when displaying calculated values such as prices or measurements.

amount = 125.6789

print(round(amount, 2))

Output

125.68

Round a Number to Three Decimal Places

You can increase the precision by changing the second argument to 3.

measurement = 12.34567

print(round(measurement, 3))

Output

12.346

Can round() Round to Tens or Hundreds?

Yes. The ndigits argument can also be negative. This allows you to round values to tens, hundreds, thousands, and other positions to the left of the decimal point.

print(round(1234, -1))
print(round(1234, -2))

Output

1230
1200

Here, -1 rounds to the nearest ten, while -2 rounds to the nearest hundred.

Common Uses of round() in Python

Rounding is useful whenever displaying or processing a number with excessive precision is unnecessary. Some common examples include:

Displaying calculated prices.
Formatting percentages.
Presenting measurements.
Simplifying mathematical results.
Preparing numerical values for reports.
Reducing unnecessary decimal digits in data analysis.

Important Points to Remember

round(number) rounds a value without specifying decimal precision.
round(number, ndigits) lets you specify the desired precision.
The ndigits parameter is optional.
Python uses round-half-to-even behavior for halfway cases.
A negative ndigits can be used to round positions to the left of the decimal point.
round() returns a numeric result rather than changing the original variable automatically.

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Conclusion

The Python round() function provides a convenient way to control the precision of numerical results. You can use it without a second argument to round a number to the nearest integer, or provide ndigits when you need a specific number of decimal places.

It is useful in calculations, data processing, measurements, reports, and many other programming situations where displaying excessive decimal digits is unnecessary. Understanding Python’s round-half-to-even rule is also important when working with values that fall exactly halfway between two possible results.

Frequently Asked Questions

How do I round a number in Python?

Use the built-in round() function:

round(12.56)

How do I round a number to two decimal places?

Pass 2 as the second argument:

round(12.5678, 2)

This produces 12.57.

How do I round a number to one decimal place?

Use 1 as the second argument:

round(12.56, 1)

How do I round a number to the nearest 10?

Use a negative value for ndigits:

round(126, -1)

The result is 130.

Does Python always round .5 upward?

No. Python uses the round-half-to-even rule for halfway cases. For example, round(5.5) gives 6, while round(6.5) also gives 6.

Can I round numbers without using round()?

Yes. Other approaches can be used depending on the requirement, including formatting techniques, mathematical operations, or libraries such as NumPy. However, round() is the built-in option for standard Python rounding.

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How to Round Numbers in Python