Math & Stats

Significant Figures Calculator

Count the significant figures in any number and round it to a chosen number of sig figs. Applies the standard rules for zeros, decimals, and scientific notation.

Significant Figures Calculator

Number

Round to (significant figures) — optional

Method

How this calculator works

Significant figures include all non-zero digits, zeros between significant digits, and trailing zeros only when a decimal point is present. Leading zeros are never significant. To round to N sig figs, keep N digits from the first non-zero digit and round the remainder.

Type a number into the input — plain decimals and scientific notation like 4.56e-3 are both accepted.
Read the significant-figure count shown as the main result.
Optionally enter a target number of significant figures to see the number rounded to that precision.

Examples

Worked examples

Real numbers, end-to-end results.

Count sig figs in 0.004560

4 significant figures

Leading zeros don't count; the trailing zero counts because a decimal point is present.

Round 3.14159 to 3 sig figs

3.14

Keep three significant digits starting at the first non-zero digit, then round.

Use cases

When to use it

Reporting laboratory measurements to the correct precision.
Checking chemistry and physics homework answers.
Rounding experimental data before publishing results.
Teaching the rules of significant digits with worked numbers.

FAQ

Frequently asked questions

What are significant figures?

Significant figures (or significant digits) are the digits in a number that carry meaningful information about its precision. They include all non-zero digits, any zeros between them, and trailing zeros when a decimal point is present.

Do leading zeros count as significant?

No. Leading zeros are only placeholders that set the decimal position. In 0.0042, the two leading zeros are not significant, so the number has two significant figures (the 4 and the 2).

Do trailing zeros count as significant?

Trailing zeros count only when a decimal point is present. In 2.500 the trailing zeros are significant (4 sig figs), but in 2500 without a decimal they are ambiguous and treated as not significant (2 sig figs).

How do I round to a number of significant figures?

Keep the requested number of significant digits starting from the first non-zero digit, then round the next digit up or down. For example, 3.14159 to 3 sig figs is 3.14, and 0.004567 to 2 sig figs is 0.0046.

Does scientific notation affect significant figures?

Scientific notation makes sig figs unambiguous. In 2.50 × 10³ only the digits in the coefficient (2.50) count, giving 3 significant figures, while the power of ten only fixes the magnitude.