Significant Figures Calculator
Count the significant figures in any number and round values to a chosen number of sig figs, with the rules explained.
Last reviewed by the Radiatus Cloud team
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Count the sig figs and round correctly
Significant figures express how precisely a number is known, and the rules for counting and rounding them trip up students and professionals alike. This calculator counts the significant figures in any number and rounds a value to a chosen number of them, applying the rules correctly so you do not have to second-guess the leading zeros.
The rules that cause the confusion
The traps are specific. Leading zeros never count, so 0.0042 has two significant figures. Trailing zeros count only when there is a decimal point, so 1200 is ambiguous but 1200. is four figures. Zeros between non-zero digits always count. These rules are simple individually and confusing together, which is exactly why a tool that applies them consistently is useful.
Precision that carries meaning
Significant figures matter because reporting more of them than you actually measured claims a precision you do not have, and reporting fewer throws away real information. In science and engineering the count communicates the reliability of a value, so getting it right is part of reporting honestly. The calculation runs in your browser.
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Frequently Asked Questions
Do leading zeros count as significant?
No. Leading zeros are never significant, so 0.0042 has two significant figures, the 4 and the 2.
When do trailing zeros count?
Only when there is a decimal point. 1200 is ambiguous, but 1200. or 1200.0 makes the trailing zeros significant.
Do zeros between digits count?
Yes. Zeros between non-zero digits are always significant, so 105 has three significant figures.
Why do significant figures matter?
Because they communicate how precisely a value is known. Reporting too many claims precision you do not have; too few discards real information.
Is my input uploaded?
No. The calculation runs entirely in your browser.
Privacy & Security
Runs entirely in your browser. No data is sent to any server.
How to Use
Type a number (decimals and scientific notation supported) to count its significant figures. Enter a sig-fig count to round it.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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