Rules for rounding numbers

Rule 1. If the digit to be dropped is less than 5, drop that digit and all other to the right of that digit.	eg - Round off 86.0234 g to 3 significant figures.	86.0 g
Rule 2. If the digit to be dropped is greater than or equal to 5, increase the value of the last digit retained by one.	eg - Round off 0.06587 L to 3 significant figures.	0.0659 L
Rule 3. If the digits to be dropped are to the left of the decimal point, zeros are used as their replacements.	eg 1- Round off 1780.1 m to 4 significant figures.	1.780 x 103 m or m Do not leave it as '1780 m' as it is confusing.
	eg 2 - Round off 25,369 g to 3 significant figures.	2.54 x 104 g OR g

Additional Rule

If the digit to be dropped is 5 and is followed by zeros, drop the 5 and

• keep the last digit as is if the digit before the '5' is even, or
• increase the last digit by 1 if the digit before the '5' is odd.

This rule is strictly applied if you are doing round off of statistical data as it prevents consistent rounding up of the data. This rule is not strictly enforced.

eg 1 - Round off 47.250 g to 3 significant figures. 47.2 g

eg 2 - Round off 47.350 g to 3 significant figures. 47.4 g

Content suitability

BCIT courses: CHEM 0011