How do you determine the number of significant figures when you make a measurement?

To determine the number of significant figures in a measurement, consider all the digits that are known with certainty plus one estimated digit. Non-zero digits are always significant, while zeros between significant digits are also counted. Leading zeros are not significant, but trailing zeros in a decimal number are. For example, in the measurement 0.00456, there are three significant figures (4, 5, and 6).