All the reliable digits and first uncertain digit in the result of a measurement are called **significant digits** or significant figures.

Example: If the length is measured, as 15.6 cm the digits 1 and 5 are reliable or certain where as 6 is uncertain or doubtful digit, so the measurement has 3 significant figures.

**General rules for determining the number of significant figures:**

- All the non-zero digits are significant.
- Example : 6543 has 4 significant figures.

- All zeros occurring in between the two non-zero digits are sig.
- Example: 6003 has 4 significant figures.

- In a number without decimal zeros on the right of non-zero digits are not sig.
- Example : 6300 has 2 significant figures.

- In a number with decimal, zeros on the right of the last no zero digits are sig.
- Example : 1.34000 has 6 significant figures.

- In a value less than 1, zeros occurring between the decimal point and non-zero digits on the right or not significant figures.
- Example : 0.0037 has 2 significant figures.

- The change in unit of measurement of quantity does not affect the number of significant figures. When some value is expressed in an exponent form the exponent does not affect the number of significant figures.
- Example: 23 * 10
^{4} has 2 significant figures.
- Example: 23 * 10
^{–4} has 2 significant figures.

## Significant Figures Rules for Arithmetic Operations

**Rules for division and multiplication :**

In division or multiplication, the final result should retain as many significant figures, as the original number involved that has the least number of significant figures.

For example: ( 22.1 × 1.344 ) ÷ 1.5 = 19.8016

In the above example, the number with the least number of significant figures is 1.5 (2 significant figures). The result should be rounded to 20 (2 significant figures).

**Significant figures rules for addition and subtraction :**

In addition or subtraction, the final result should retain as many decimal places as the number with the least decimal places.

For example: 30.15 + 3.1 + 10.344 = 43.594

In the above example, the number with the least decimal places is 3.1 (1 decimal place), therefore your result should be rounded to 43.6 (3 significant figures).

Use our free Significant figures calculator to calculate the figures.