J4

Significant figures (sf)
Significant figures (also called significant digits) of a number are those digits that carry
meaning contributing to its accuracy.
Rules for counting significant figures are summarized below:
1. All non-zero digits are considered significant. E.g 123.45 has five significant figures:
1, 2, 3, 4, 5.
2. Zeros appearing anywhere between two non-zero digits are significant. E.g. 101.12
has five significant figures: 1, 0, 1, 1, and 2.
3. Leading zeros are not significant. For example, 0.00012 has two significant figures: 1
and 2.
4. Trailing zeros in a number containing a decimal point are significant. For example,
12.2300 has six significant figures: 1, 2, 2, 3, 0 and 0. The number 0.00122300 still
has only six significant figures (the zeros before the 1 are not significant). In addition,
120.00 has five significant figures.
5. Trailing zeros in a number not containing a decimal point are not significant. For
example 470,000 has two significant figures.
Examples
Rounding to 2 s.f:
1. 12300 becomes 12000
2. 13 stays as 13.
3. 0.00123 becomes 0.0012
4. 0.1 becomes 0.10, the trailing zero indicates that we are rounding to 2 s.f
5. 0.0125 becomes 0.013
6. 19800 becomes 20000.