Rules for Counting Significant Figures

 

 

1. Nonzero integers always count as significant figures

 

ex. 1.23 has 3 significant figures

 

2. Zeros there are three kinds of zeros

 

a. Leading zeros zeros to the left of nonzero digits

- never count as significant figures

 

ex. 0.0025 has 2 significant figures

 

b. Captive zeros zeros between nonzero digits

- always count as significant figures

 

ex. 1.008 has 4 significant figures

 

c. Trailing zeros zeros to the right of nonzero digits

- only count if the number contains a decimal

 

ex. 100 has 1 significant figure

 

ex. 1.00 x 102 has 3 significant figures

 

ex. 100. has 3 significant figures

 

3. Exact numbers have an infinite number of significant figures

 

a. counted numbers

 

ex. 10 experiments, 3 apples or 8 molecules have an infinite

number of significant figures

 

b. defined numbers

 

ex. 1 kilogram = 1,000 grams have an infinite number of

significant figures