Rounding off Data – (Chemistry XI)


As we discuss in previous topic, the Significant Figure are those digits in a measured number that include all certain digits plus (0) final are with having with uncertainty.

Significant Figures

  • DO round off means to reduce a number to the desired number of significant figure.
  • It is a process of dropping a non-significant digits in any calculation and adjusting the last uncertain reported digit in order to get the extra right one answer according to certain rules:

Electronic Configuration

Rules for Rounding Off Data:

There are three rules for rounding off data according to number scale.

1,2,3,4 Rule-1

, 5, Rule-3

6,7,8,9 Rule-2


If the digit to be dropped or going to be rounded off is greater than 5 then we will add 1 to the second last digit: for example: 5.8986, in this number last digit is (6) and which is greater than 5, so we will add (1) in second last digit and now the figure will be: 5.899, and this number has 4 significant figures.


If the digit to the dropped or going to be rounded off is lesser than 5, then we will simply drop that digit without doing any thing and the value would be same.  for example: 5.13893, in this figure the last digit is (3) which is lesser than 5, so we will simply drop this 3, and final figure will be as 5.1389, Which have 5 significant figures.


When the last digit is 5, then we have to follow following two rules: (i). If the second last digit is odd number than we have to add (1) in that number. (ii). If the second last digit is even the we should leave same number.


(i). 5.68915 (in this figure second last digit is (1) so we have to add 1 in this number by removing the last digit 5, (5.6892)

(ii). 5.68925 ((in this figure second last digit is (2) so we have to leave it as it is and just drop last digit 5, (5.6892)