Significant figures are the number of digits of a number that are known with a certain degree of precision, for example, a burette reading of 15.25 cm^{3} has 4 significant figures, while the reading of 0.084 g for the mass of an object has 2 significant figures. The rules that determine the number of significant figures in a number are:

 Zeros preceding the first nonzero digit of a number are not significant, e.g. 0.084 and 0.1 have 2 and 1 significant figures respectively.
 Zeros in between nonzero digits of a number are significant, e.g. 1005 and 1.005 have 4 significant figures each.
 Zeros trailing the last nonzero digit of a decimal are significant, e.g. 2.3400 and 0.2300 has 5 and 4 significant figures respectively.
 Zeros trailing the last nonzero digit of a positive or negative integer may or may not be significant, e.g. 2500 may have 2 or 3 or 4 significant figures. To avoid confusion, such numbers should be expressed in standard form, e.g. 2.5 x 10^{3}, 2.50 x 10^{3} and 2.500 x 10^{3} have 2, 3 and 4 significant figures respectively.