CHEM 121 - Signficant Figures (SF) rules + calculation rules

Are non-zero digits significant?

Yes. Non-zero digits are always significant.

How many significant figures are in 357?

3 significant figures.

How many significant figures are in 91?

2 significant figures

Are zeros between non-zero digits significant?

Yes. Zeros between non-zero digits are significant.

How many significant figures are in 101?

3 significant figures.

How many significant figures are in 5006?

4 significant figures.

Are leading zeros significant?

No. Leading zeros are not significant. They only show the position of the decimal.

How many significant figures are in 0.0025?

2 significant figures.
(Scientific notation: 2.5 × 10⁻³)

How many significant figures are in 0.00030?

2 significant figures.
(Scientific notation: 3.0 × 10⁻⁴)

Are trailing zeros significant?

Only if there is a decimal point

How many significant figures are in 250.00?

5 significant figures.

How many significant figures are in 2500.?

4 significant figures.

How many significant figures are in 2500?

2 significant figures

How many significant figures are in 2,000?

1 significant figure

significant figures in calculations

Addition and subtraction rule

result has the same # of decimal places as the measurement with the fewest decimal places

• exp. 2.102 + 61.09 + 3.0 = 66.122 → 66.1

• ^ smallest # (tenths)

significant figures in calculations

multiplication and division rule

The result carries the same # of significant figures as the measurement with the fewest significant figures

• exp. 24.66cm * 0.35cm = 8.631 → 8.6 cm²

• ^ 4 SF ^ 2 SF (smallest)

• exp. 21.5cm * 0.30cm / 1.88cm = 3.43085 → 3.4cm

• ^ 3 SF ^ 2 SF ^ 3 SF