Significant Figures Calculator
Round to a chosen number of significant figures and count the sig figs in a value.
What the Significant Figures Calculator does
Significant figures record how precisely a value is known. Leading zeros never count, digits between non-zeros always do, and trailing zeros count only after a decimal point.
Formula
Keep the first n non-zero digits, then round based on the next digit
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Number | number | Yes | — |
| Significant figures | number | Yes | Accepts 1 or more, up to 15. |
How to use it
- Enter Number and Significant figures.
- Select Calculate.
Worked example
Report 0.0045678 to 3 significant figures.
- Number
- 0.0045678
- Significant figures
- 3
0.00457 — the leading zeros do not count, so the significant digits are 4, 5 and 7.
Reading the result
- Significant figures record how precisely a value is known, not how many digits it has. 0.00420 has three.
- A calculated result cannot be more precise than its least precise input, which is what limits how many figures you may keep.
Common mistakes
- Counting leading zeros. They only place the decimal point and are never significant.
- Keeping every digit a calculator shows. Reporting 12 figures from measurements known to three claims a precision that was never measured.
Frequently asked questions
How many sig figs should a calculated result have?
For multiplication and division, match the input with the fewest significant figures. For addition and subtraction, match the fewest decimal places.