In our other two calculators involving significant figures (Get and Set the Number of Significant Figures and Convert Numbers between Decimal, Scientific, and Exponential Notation), we highlighted the importance of using correct significant figures when reporting experimental parameters. It is also important to know how to handle significant figures when performing mathematical operations such as addition, subtraction, multiplication, and division. The calculator below takes two numbers as its input and allows you to determine the correct number of significant figures when the two numbers are added, subtracted, multiplied, or divided.

Two (2) simple rules allow us to determine the correct number of significant figures when performing mathematical operations such as addition, subtraction, multiplication, and division.

As it can be seen from the two rules above, rounding significant figures in additions and subtractions is not as simple as it is for multiplications and divisions. Use the calculator below and try many different input numbers to develop a good feel for these operations. The image above also shows a few additional examples.

This calculator allows you to determine the number of significant figures for the resulting calculation when two numbers are added, subtracted, multiplied, or divided. Numbers may be entered in one of three formats (decimal notation, scientific notation, or exponential notation), and the calculator will output that number in all three formats, and will highlight the significant figures of the resulting calculation. A decimal is a number expressed in base-ten numeral system. Examples of decimals are 123, 98.69, −659.821, 10359.659586, and 0.0123456789. A decimal, such as 123, expressed in scientific notation has the following format: 1.23 × 10² (assuming 3 significant figures). 123 expressed in exponential (e) notation has the following format: 1.23e2 ( e  may also be capitalized, i.e., 1.23E2).

For the purpose of using the calculator below, it is straightforward to enter numbers in decimal notation and in exponential notation. They may be entered exactly as they appear. Commas may also be entered as thousand separators. For exponential notation, there should not be a space before or after  e . To enter numbers in scientific notation, use the  x  character (letter  x ; lower or upper case) or  *  character (asterisk) for the multiplication symbol, and use the  ^  character (caret) to indicate the power to which 10 should be raised. For example, 1.23 × 10² may be entered as 1.23 x 10^2. Spaces do not make a difference, so this is fine as well: 1.23x10^2. The asterisk character may also be used, so this will also work: 1.23 * 10^2.