--- title: 3.10 Rounding Numbers description: "Rounding is the process of reducing the number of digits in a number while keeping its value as close as possible to the original. Python provides the built-in `round()` function to round numbers. Rounding is commonly used when displaying measurements,…" url: "https://edcret.in/docs/python-programming/numeric-data-types-python/3-10-rounding-numbers/" updated: "2026-07-29" category: Python Programming / Numeric Data Types --- # 3.10 Rounding Numbers Rounding is the process of reducing the number of digits in a number while keeping its value as close as possible to the original. Python provides the built-in `round()` function to round numbers. Rounding is commonly used when displaying measurements, prices, percentages, averages, and other values where excessive decimal places are unnecessary. --- ## Syntax ``` round(number) ``` or ``` round(number, digits) ``` ### Parameters | Parameter | Description | | --- | --- | | `number` | The number to be rounded. | | `digits` *(Optional)* | Number of decimal places to keep. If omitted, Python rounds to the nearest integer. | ### Return Value Returns the rounded value. --- ## Example 1: Rounding to the Nearest Integer **main.py** ``` number = 7.6 print(round(number)) ``` ### Output ``` 8 ``` ### Explanation - `7.6` is closer to `8` than `7`. - Therefore, `round()` returns `8`. --- ## Example 2: Rounding Down **main.py** ``` number = 7.3 print(round(number)) ``` ### Output ``` 7 ``` ### Explanation - `7.3` is closer to `7`. - Therefore, the rounded result is `7`. --- ## Example 3: Rounding to Two Decimal Places **main.py** ``` pi = 3.14159265 print(round(pi, 2)) ``` ### Output ``` 3.14 ``` ### Explanation - The second argument specifies the number of decimal places. - The value is rounded to two digits after the decimal point. --- ## Example 4: Rounding to Three Decimal Places **main.py** ``` value = 12.987654 print(round(value, 3)) ``` ### Output ``` 12.988 ``` ### Explanation - The number is rounded to three decimal places. - The fourth decimal digit determines whether the third digit is increased. --- ## Example 5: Rounding an Integer **main.py** ``` number = 125 print(round(number)) ``` ### Output ``` 125 ``` ### Explanation - Integers do not have decimal places. - Therefore, the value remains unchanged. --- ## Example 6: Rounding Negative Numbers **main.py** ``` number = -8.6 print(round(number)) ``` ### Output ``` -9 ``` ### Explanation - The `round()` function also works with negative numbers. - `-8.6` is closer to `-9` than to `-8`. --- ## Example 7: Rounding User Input **main.py** ``` number = float(input("Enter a decimal number: ")) print(round(number, 1)) ``` ### Sample Input ``` 45.678 ``` ### Output ``` 45.7 ``` ### Explanation - `float()` converts the user input into a floating-point number. - `round(number, 1)` keeps one digit after the decimal point. --- ## Example 8: Rounding in Calculations **main.py** ``` average = (82 + 91 + 76) / 3 print(round(average, 2)) ``` ### Output ``` 83.0 ``` ### Explanation - The average is calculated first. - The result is then rounded to two decimal places. - Since the result already has one decimal place, no additional digits appear. --- ## Example 9: Rounding to Tens **main.py** ``` number = 276 print(round(number, -1)) ``` ### Output ``` 280 ``` ### Explanation - A negative value for the second argument rounds digits to the left of the decimal point. - `-1` rounds to the nearest multiple of 10. --- ## Example 10: Rounding to Hundreds **main.py** ``` number = 864 print(round(number, -2)) ``` ### Output ``` 900 ``` ### Explanation - `-2` rounds to the nearest hundred. - Since `864` is closer to `900` than to `800`, the result is `900`. --- # Common Mistakes ### 1. Assuming `round()` Always Returns a Float **Incorrect** ``` print(type(round(8.6))) ``` ### Incorrect Expectation ``` ``` ### Actual Output ``` ``` **Reason** When no second argument is provided, `round()` returns an integer if the result is an integer. --- ### 2. Forgetting the Parentheses **Incorrect** ``` print(round) ``` ### Output ``` ``` **Reason** `round` is the function object itself. **Correct** ``` print(round(5.7)) ``` --- ### 3. Passing a String Directly **Incorrect** ``` print(round("3.14")) ``` ### Output ``` TypeError: type str doesn't define __round__ method ``` **Reason** `round()` expects a numeric value. **Correct** ``` print(round(float("3.14"))) ``` --- ### 4. Expecting `round()` to Modify the Variable **Incorrect** ``` number = 5.78 round(number) print(number) ``` ### Output ``` 5.78 ``` **Reason** `round()` returns a new value. It does not modify the original variable. **Correct** ``` number = round(number) print(number) ``` --- # Best Practices - Use `round()` when displaying values to users. - Specify the required number of decimal places instead of relying on the default behavior. - Store the returned value if it will be used later. - Convert user input to a numeric type before rounding. - Use negative values for the second argument when rounding to tens, hundreds, or thousands. --- # Key Points to Remember - Python provides the built-in `round()` function for rounding numbers. - Without a second argument, `round()` rounds to the nearest integer. - The optional second argument specifies the number of decimal places. - Negative values for the second argument round digits to the left of the decimal point. - `round()` works with both integers and floating-point numbers. - `round()` returns a new value and does not modify the original variable. - Convert strings to numeric types before passing them to `round()`.