The significant figures of numbers are digits convey the meaning that contributes to its measurement resolution. The number 13.2 is comprised of three significant digits. Non-zero digits are always significant. 3.14159 has 6 significant digits (all the numbers give you useful information). Thus, 67 has 2 significant digits, and 67.3 has three significant digits.

1000 has 1 significant digit. Similarly for decimals, 0.00069 has 2 significant digits. But this rule has an exception, as in the case of 0.000690 has 3 significant digits. One thousand six (1006) has 4 significant digits.

Application of Significant Figures

These examples can be incorporated into a list of rules for Significant Figures;

  1. All nonzero digits are significant: 4.321 g has four significant figures.
  2. Zeroes between nonzero digits are significant: 1002 kg has 4 figures.
  3. Leading zeros to the left of the first nonzero digits are not significant.
  4. Trailing zeroes that are also to the right of a decimal point in a number are significant: 0.0260 mL has three significant figures.
  5. When a number ends in zeroes that are not to the right of a decimal point, the zeroes are not necessarily significant: 140 kilometres may be 2 or 3 significant figures.

To resolve this confusion presented by the last rule, we can use the standard exponential representation of the numbers. For example,

3.69 × 104 calories (3 significant figures)

3.069 × 104 calories (4 significant figures)

Exact Number

Some numbers are known with certainty like there are 12 inches in a foot or there are 50 students in a class. Such measurements do have scope for uncertainty. Exact numbers are often found as conversion factors or as counts of objects.