Significant Figures Calculator

Enter Calculation

Number

Round to how many significant figures?

Results

Significant Figures in the Number

5

significant digits

Rounded to 3 sig figs	0.00456
Requested precision	3 sig figs

What Is a Significant Figures Calculator?

Significant figures (sig figs) are the digits in a number that carry real measurement meaning. This calculator does two jobs at once: it counts how many significant figures a number contains, and it rounds that number to a precision you choose. It's a universal math tool used in chemistry, physics, engineering and everyday science homework — no country or unit assumptions apply.

How to Use It

Enter the number exactly as written (keep trailing zeros and the decimal point, since they affect the count). Then choose how many significant figures you want to round to. The result shows the sig-fig count of your original number plus the rounded value.

The Rules Explained

The counting rules are: (1) every non-zero digit is significant; (2) zeros between non-zero digits are significant; (3) leading zeros are never significant; (4) trailing zeros are significant only when the number contains a decimal point. For rounding, we find the power of ten needed so that the first n significant digits sit just before the decimal, round to the nearest whole number, then scale back.

$$\text{Rounded} = \frac{\operatorname{round}\!\left(\text{Number} \times 10^{\,p}\right)}{10^{\,p}} \qquad p = \text{Sig figs} - \left\lceil \log_{10}\left|\text{Number}\right| \right\rceil$$

The core rules: non-zero digits and sandwiched zeros count, leading zeros never count.

Worked Example

Take 0.0045600. The leading zeros (0.00) are not significant. The remaining digits 4, 5, 6, 0, 0 are all significant because a decimal point is present, giving 5 significant figures. Rounding this same value to 3 sig figs scales it to \(4.56\), rounds, and scales back to 0.00456.

Rounding to a set number of significant figures snaps the value to the nearest step.

FAQ

Are trailing zeros always significant? Only when a decimal point is shown. "1500" counts as 2 sig figs, but "1500." or "1500.0" counts more.

Does the calculator handle negative numbers? Yes — the sign is ignored for counting and rounding, then preserved in the result.

Why does rounding 0.0045600 to 3 sig figs show 0.00456? Trailing display zeros may be dropped in plain decimal output, but the value and its 3-sig-fig precision are correct.