About this significant figures calculator
This significant figures calculator helps you either count how many significant figures (sig figs) a number has or round a value to a fixed number of significant figures (3 by default). Significant figures indicate the precision of a measurement or calculated result. They are widely used in science, engineering, and lab work to avoid overstating accuracy. Enter a number such as 123.45, 0.0050, or 1.23e4, choose the operation, and click Get result to see the count or rounded value with a short explanation.
The calculator follows standard rules: all non-zero digits are significant; zeros between non-zero digits are significant; leading zeros are not significant; trailing zeros after a decimal point are significant; and trailing zeros in whole numbers are ambiguous unless written in scientific notation. For rounding, the tool uses these rules to keep the requested number of sig figs while preserving the magnitude of the number. It supports both ordinary decimal notation and scientific notation (e.g. 1.23×10⁴ written as 1.23e4), which is often used to clearly indicate how many digits are significant.
Significant figures matter because they keep your reported results consistent with the precision of your measurements or given data. In multiplication and division, the result should have as many significant figures as the factor with the fewest sig figs; in addition and subtraction, the limiting factor is decimal places instead. This calculator is a quick way to check how many significant figures a value has or to round results appropriately for lab reports, homework, and scientific calculations. It is free, mobile-friendly, and runs entirely in your browser, so you can use it on phones, tablets, or desktops whenever you need to check sig figs.