Rules of Significant Figures

The certainty of measurement depends on two factors: the number of digits in the measurement and the precision of the instrument used.

In a measured quantity, all of the digits, including the last uncertain digit, are called significant figures - and can be determined using specific rules.

Any non-zero digits and all captive zeros - which lie between two non-zero digits - are significant. For example, 28 has two significant figures, while 26.25 has four, and 208 has three.

Leading zeros are never significant, as they just locate the decimal point. For example, 0.00208 has three significant figures. Such quantities can be expressed using exponential notations. Thus, 0.00208 can be written as 2.08 × 10⁻³.

Trailing zeros are only significant in decimal formatted numbers. 2200 has two trailing zeros and two significant figures, whereas 2200.0 and 2200.1 both have 5 significant figures.

For quantities without decimal points, the significance of trailing zeros becomes ambiguous. Thus, 2200 can be written as 2.2 × 10³ with two significant figures or 2.20 x 10³ with three significant figures.