The Significant Figures Calculator does two jobs students and lab workers need constantly: it counts how many significant figures a number already has, and it rounds a number to a chosen number of significant figures. Both follow the standard rules taught in chemistry, physics and engineering.
The rules it uses
- Non-zero digits are always significant. 12.5 has three.
- Zeros between significant digits are significant. 1002 has four.
- Leading zeros are never significant. 0.0045 has two — the zeros only fix the decimal place.
- Trailing zeros after a decimal point are significant. 2.300 has four, which is why writing the zeros matters in a measurement.
- Trailing zeros in a bare whole number are ambiguous. 4500 could be two, three or four sig figs. The tool counts the minimum and suggests scientific notation when the zeros are meant to count.
Rounding to N significant figures
Rounding to significant figures keeps a fixed number of meaningful digits rather
than a fixed number of decimal places. For example 3.14159 rounded to three
significant figures is 3.14, and 0.00204857 to three is 0.00205. The tool uses
the language’s exact toPrecision rounding so the result always carries the
requested number of digits.
Worked examples
| Number | Significant figures |
|---|---|
| 100.0 | 4 |
| 0.00320 | 3 |
| 5.006 | 4 |
| 1.20 × 10³ | 3 |
Enter any of these above to confirm the count, then switch to round mode to trim a long calculation result down to the precision your data justifies.