How to round decimals ? | Rounding Numbers Guide

Arrondir un nombre
Teenage girl helping classmate with mathematics and explaining him how to solve equations

How do you know when to round up decimals ?

When dealing with decimal numbers, rounding is an important concept that everyone should master. Rounding is useful in different situations: rounding to pay bills or in an academic setting to find out the estimate of the average score of students in a class.

Rounding decimals consists of rounding a decimal number to a certain number of decimal places, to save time and help us express really long numbers in shorter terms. We can round decimals to the nearest wholes, tenths or hundredths, when having exact values isn’t important. A rounded number has almost the same value as the original number but it is a bit less exact.

There are certain rules to follow when rounding a decimal number. Put simply, if the last digit is less than 5, round the previous digit down. However, if it’s 5 or more than you should round the previous digit up. So, if the number you are about to round is followed by 5, 6, 7, 8, 9 round the number up. And if it is followed by 0, 1, 2, 3, 4 round the number down.

Need a tutor in math?

Rounding Example

Consider the number 5.9163

5.9163 rounded to the nearest tenth is 5.9

  • Because 9 is followed by 1 and 1 is less than 5.

5.9163 rounded to the nearest hundredth is 5.92

  • Because 1 is followed by 6 and 6 is greater than 5.

5.9163 rounded to the nearest thousandth is 5.916

  • Because 6 is followed by 3 and 3 is less than 5.

How to round to two decimal places?

Rounding decimals to two decimal places is the same as rounding to the nearest hundredth.  To round a number to the nearest hundredth, look at the digit at the right of the hundredth place and apply the same rule : if the digit in the thousandth place is 0, 1, 2, 3, 4, you will round down to the nearest hundredth or just remove all digits found at the right. But, if the digit in the thousandth place is 5, 6, 7, 8, 9, you have to round up to the nearest hundredth, and then remove all the digits on the right.

Rounding Example 1

Consider the number 8.254

8.254 rounded to two decimal places is 8.25

  • Because 5 is followed by 4 and 4 is less than 5.

Rounding Example 2

Consider the number 4.738

4.738 rounded to the nearest hundredth (two decimal places) is 4.74

  • Because 3 is followed by 8 and 8 is greater than 5.

How to round to 4 decimal places?

Rounding decimals to four decimal places refers to rounding to the nearest ten thousandth. To round a decimal number to the nearest ten thousandth, look at the digit one place to the right of the fourth place (look at the 5th place), if the digit there is 5 or greater, you round up to the nearest ten thousand; and if the digit in the 5th place is less than 5, you round down to the nearest ten thousand or you just remove all the digits after the fourth place.

Example 1

For this example, we will consider the number π , which equals to 3.1415926…

3.1415926 rounded to four decimal places (nearest ten thousandth) is 3.1416

  • Since the number in the 5th place is 9, which is greater than 5.

Example 2

For this, we will take the number 20.35784

20.35784 rounded to the nearest ten thousandth is 20.3578

  • As the number after the fourth place is 4, which is less than 5.

Need help in mathematics? 

{
“@context”: “https://schema.org”,
“@type”: “FAQPage”,
“mainEntity”: [{
“@type”: “Question”,
“name”: “How do you know when to round up decimals ?”,
“acceptedAnswer”: {
“@type”: “Answer”,
“text”: “Put simply, if the next digit is less than 5, round the previous digit down; if it’s 5 or more than round the previous digit up.

So, if the number you are about to round is followed by 5, 6, 7, 8, 9 round the number up and if it is followed by 0, 1, 2, 3, 4 round the number down.”
}
},{
“@type”: “Question”,
“name”: “How to round to two decimal places ?”,
“acceptedAnswer”: {
“@type”: “Answer”,
“text”: “If the digit in the thousandth place is 0, 1, 2, 3, 4, you round down to the nearest hundredth and if it is 5, 6, 7, 8, 9, you round up to the nearest hundredth.”
}
},{
“@type”: “Question”,
“name”: “How to round to 4 decimal places ?”,
“acceptedAnswer”: {
“@type”: “Answer”,
“text”: “Look at the digit at the right of the fourth place, if it’s 5 or greater, you round up to the nearest ten thousand and if it’s less than 5, you round down to the nearest ten thousand.”
}
}] }