The significant figures in measurement or result are the number of digits known with certainty plus one uncertain digit.
Rules for deciding significant figures:
- All non-zero digits are significant.
e.g. 127.34 g contains five significant figures which are 1, 2, 7, 3, and 4.
- All zeros between two non-zero digits are significant.
e.g. 120.007 m contains six significant figures.
- Zeros on the left of the first non-zero digit are not significant. Such a zero indicates the position of the decimal point.
e.g. 0.025 has two significant figures, 0.005 has one significant figure.
- Zeros at the end of a number are significant if they are on the right side of the decimal point.
e.g. 0.400 g has three significant figures and 400 g has one significant figure.
- In numbers written in scientific notation, all digits are significant.
e.g. 2.035 × 10^{2} has four significant figures and 3.25 × 10^{–5} has three significant figures.