Python provides many math methods for mathematical operations such as square roots, exponents, and so on.
In this article, I will show you how to round up a number to a specified decimal place.
What is a Decimal Place?
Look at this number: 324.89.
Each number here has a position which is refered to as place value. The place value of:
- 3 is hundreds
- 2 is tens
- 4 is ones
- 8 is tenths
- 9 is hundredths
After the decimal point, you have two numbers: 8, then 9. The decimal place of a number is the position of the number after a decimal point (on the right side of it).
This definition means that the decimal place of 8 (in the tenths position) is 1, and 9 (in the hundredths position) is 2.
How to Round Up to a Certain Decimal Place
What does it mean then to round up to a certain decimal place? It means that you round up a number at a decimal place based on the number after it.
If the number after the decimal place is 5 or more, the number at the decimal place is rounded up +1. Otherwise, the number at the decimal place stays the same and the number after the decimal place is rounded down to 0.
For example, let's say we want to round up 24.89 to 1 decimal place. Or you can put it as rounding up 24.89 to the nearest tenth.
The number 8 is at the 1 decimal place, and the number after 8 is 9. Since 9 is more than 5, 24.89, rounded up to the nearest tenth will be 24.9.
As another example, let's take 24.82 and round it to 1 decimal place (the nearest tenth). Since 2 is not larger than 5, 8 remains the same, and 2 gets rounded down – resulting in 24.8.
How to Round Up a Decimal Place in Python
Now that you understand how to round up a decimal place, let's see how to do it in Python.
You can use the global round function to round up numbers to a decimal place. The syntax is:
round(number, decimal_point)
The function accepts the number and decimal_point as arguments. decimal_point specifies the decimal place that you want to round the number up to. Let's see an example:
num = 24.89
rounded = round(num, 1)
print(rounded)
# 24.9
Here's another example of a longer number:
num = 20.4454
rounded3 = round(num, 3)
# to 3 decimal places
rounded2 = round(num, 2)
# to 2 decimal places
print(rounded3)
# 20.445
print(rounded2)
# 20.45
For rounded3, the num is rounded up to 3 decimal places. At the 3rd decimal place is 5, and the number that comes after it is 4. Since 4 is not greater than 5, the number 5 stays the same and 4 is rounded down to 0.
For rounded2, the num is rounded up to 2 decimal places. At the 2nd decimal place is 4, and the number after it is 5. Since this number is greater than or equal to 5, the number 4 is rounded up to 5.
Conclusion
Rounding up numbers can be useful for keeping floating numbers within fixed digits.
For example, this is useful with currencies that only accept two decimal places (like the dollar: $100.99). In cases where a calculation for a product results in $50.678, you may want to round it to 2 decimal places, like this: $50.68. This way, it can be easier to give someone the actual monetary value.
In this article, I've briefly explained what decimal places are, and how to round numbers to certain decimal places in Python.