Chemistry / Unit 1: Matter and Measurement
1.5 Significant Figures
Notes
Significant figures (sig figs) are the digits in a measurement that are known, plus one estimated digit.
- Nonzero digits are always significant. Zeros between nonzero digits count: 205 has 3.
- Leading zeros never count: 0.0045 has 2. Trailing zeros count only if there is a decimal point: 2.500 has 4, 2500 has 2.
- Multiplying and dividing: round to the fewest sig figs. Example: $2.50 \times 3.1 = 7.75 \rightarrow 7.8$.
- Adding and subtracting: round to the fewest decimal places. Example: $12.11 + 0.3 = 12.41 \rightarrow 12.4$.
Practice
How many significant figures are in 0.004050?
Leading zeros do not count. The 4, 0, 5 and final 0 (after a decimal) do: 4 sig figs.
Calculate $4.82 \times 1.6$ with the correct number of significant figures.
$4.82 \times 1.6 = 7.712$. The answer can have only 2 sig figs, like 1.6.
Calculate $15.2 + 3.456$ with correct significant figures.
Round to the fewest decimal places (one, from 15.2): 18.656 becomes 18.7.
Ready for more? Take the Unit 1 test.