Using the Significant Figures Calculator
Enter measured values exactly as recorded, including decimal points and trailing zeros. Choose an operation to see the rounded answer and the precision rule used for that calculation.
Worked example
Use the example inputs below to reproduce this result. These are the form's starting values, not recommended targets. Changing your inputs updates your result above; this worked example stays fixed for comparison. Results are rounded for display.
Example inputs
- First measured number
- 1.20
- Operation
- +
- Second measured number
- 0.003
Example result
- Rounded result (precision preserved)
- 1.20e+0
- First input significant figures
- 3
- Second input significant figures
- 1
- Rounding rule
- Add/subtract: round to the least precise place, 10^-2.
Method and assumptions
Addition/subtraction uses the least precise decimal place; multiplication/division uses the fewest significant figures. Integer trailing zeros without a decimal point are treated as non-significant: write 1200. or 1.200e3 to specify four. Inputs are treated as measurements, not exact constants. Results use scientific notation to preserve zeros; 15 significant figures maximum.
Reference: calculatorsoup.com — method and further reading
Distinguish notation from value
A number can be written in more than one system without changing its value. Conversion changes the representation, while arithmetic changes the number itself. This tool uses one documented notation convention and a limited range. A historical inscription or decorative variant may require interpretation beyond that convention.
Common question
Why do addition and multiplication use different rounding rules?
Addition and subtraction depend on the least precise place value. Multiplication and division depend on the fewest significant figures among the measurements. Exact counting constants are not modeled here.