SIGNIFICANT FIGURES RULES

GENERAL RULES[1]

  1. All non-zero digits are significant.

  1. All zeros between non-zero digits are significant.

  1. All zeros at the left of the number are NOT significant.

When zeros are at the right of the number: 

  1. If there is no decimal, the zeros are NOT significant.

  1. If there is a decimal, the zeros ARE significant.

MULTIPLYING/DIVIDING:  

Round to the number of significant figures as the number that has the fewest numbers

Examples:          4.00   x    3  =     12      →       10

                            3 s.f.    1 s.f.      2 s.f.  round to 1 s.f.

                        60.0    ÷     20.0   =  3         →    3.00

                        3 s.f.              3 s.f.     1 s.f.  round to 3 s.f.

ADDING/SUBTRACTING:  

Round to the PLACE that is the least precise coming in.  (choose the place of the last SIGNIFICANT digit)

Examples:      40.56  (hundredths place)

                          9.4        (tenths place)← least precise

                +        117.321   (thousandths place)

                           167.281  round to 167.3 (tenths place)

                

                        110   (tens place)

                     -        65.4  (tenths place)

                        44.6 round to 40 (tens place)


[1] “Stoichiometry Tutorials.” Significant Figures. Accessed 25 Oct. 2018.