Rounding Numbers

Rule 1 Determine the digit you want to round off, then look at the number after it.   If the number after is 1, 2, 3 or 4 drop all digits to...

Rule 1

Determine the digit you want to round off, then look at the number after it.  

If the number after is 1, 2, 3 or 4 drop all digits to the right of the rounding digit.

Examples:

rounding 3.423 to 3 significant figures it will be 3.42

rounding 3.423 to 2 significant figures it will be 3.4

rounding 3.423 to 1 significant figure it will be 3

Rule 2

Determine the digit you want to round off, then look at the number after it.  

If the highlighted digit is 5, 6, 7, 8, 9 add one to the rounding digit and drop all digits to the right of it.

Examples:

rounding 2.786 to 3 significant figures it will be 2.79

rounding 2.786 to 2 significant figures it will be 2.8

rounding 2.786 to 1 significant figure it will be 3

rounding 2.856 to 2 significant figures it will be 2.9

Exception to Rule 2

When the digit dropped is 5 and there are no digits following or the digits following are zeros, make the preceding digit even.

Examples:

rounding 2.315 to 3 significant figures it will be 2.32

rounding 2.325 to 3 significant figures it will be 2.32

Example:

Rounding 74 to 1 significant figure

If you have 2 or more calculation steps do not round in every step. It will introduce errors. You can save the result in the memory of your calculator or use 2 digits pass the last significant figure. Then, round at the end.