Number of Significant Figures

RULE #1 - All digits 1 through 9 are significant

If the mass of an object is measured as 12.3 g, this means that the mass is known to lie between 12.2 and 12.4 g. There are 3 significant figures in 12.3.

If the mass of an object is measured as 12.3456 g, this means that the mass is known to lie between 12.3455 and 12.3457 g. There are 6 significant figures in 12.3456.

RULE #2 - Zero is significant when it is between two non-zero digits.

The quantities 306, 30.6, 3.06 and .306 all contain 3 significant figures since the 0 between the 3 and 6 is significant.

RULE #3 - A terminal zero to the right of a decimal point in a number greater than one is significant.

The quantities 279.0, 27.90 and 2.790 all contain 4 significant figures.

RULE #4 - A terminal zero to the right of a decimal point in a number less than one is significant.

The quantities .2790 and .27900 have 4 and 5 significant figures respectively.

RULE #5 - A zero used to fix a decimal point in a number less than one is not significant.

The quantities 0.456, 0.0456 and 0.00456 all contain 3 significant figures.

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