The purpose of rounding a number is to adjust the final value to be less precise. This is required when a measured or calculated result produces a number that appears more precise than the measurement can actually provide.
An example of this would be an instrument that may produce a result with 4 digits after the decimal such as 1.0043. But if that instrument is only precise to the 2nd decimal place (hundredth place), the last 2 digits of that number are not precise enough to be reported. In this case, the result would be rounded up to the hundredth place and would be reported as 1.00. See the image to identify digit placement and digit place naming.
These rounding rules apply to rounding whole numbers and decimals.
- If the digit being rounded is followed by a 6, 7, 8, or 9, the digit is rounded up.
- An example is 37 rounded to the nearest tens place would be rounded up to 40.
- If the digit being rounded is followed by a 0, 1, 2, 3, or 4, the digit is rounded down.
- An example is 342.2 rounded to the nearest ones place would be rounded down to 342.
- If the digit being rounded is followed by a 5, it will either be rounded up or down depending on if it is an even or an odd number. If the digit before the 5 is an odd number, it will be rounded up. If the digit before the 5 is an even number, it will be rounded down.
- The easiest way to remember this rule is that if you are rounding a number followed by a 5, that number will either become even or stay even.
- An example is 0.2375 rounded to the thousandth place. The thousandth place is where the 7 is located. Since the 7 is followed by a 5, you will round up as the 7 is an odd number. The result is then 0.238.
Here are some other examples:
- 1.23 rounded to the ones place would be 1
- 7,252.4 rounded to the nearest hundreds place would be 7,300
- 6.392 rounded to the nearest hundredth place would be 6.39
- 78,693 rounded to the nearest thousands place would be 79,000
- 0.00389 rounded to the nearest thousandth place would be 0.004
- 634.5 rounded to the ones place would be 634
- 2.485 rounded to the hundredth place would be 2.48
- 1375.11 rounded to the tens place would be 1380
