Significant figures are the meaningful digits which are known with certainty plus one which is estimated or uncertain. They are used to indicate the uncertainty in experimental or calculated values.

The uncertainty is indicated by writing the certain digits and the last uncertain digit. For example, if we write a result as 11.2 mL, we say the 11 is certain and 2 is uncertain, and the uncertainty would be $\pm 1$ in the last digit. Unless otherwise stated, an uncertainty of $\pm 1$ in the last digit is always understood.