Know exactly how precise your number is.
Type any number to count its significant figures, round it to as many sig figs as you want, and see it written in unambiguous scientific notation.
Your number
What this means
Rounded to fewer significant figures
| Sig figs | Rounded value | Scientific notation |
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How significant figures work
Rules for Counting Significant Figures
All non-zero digits are significant. Zeros between non-zero digits are significant (e.g., 105 has 3 sig figs). Leading zeros are never significant (0.0045 has 2 sig figs). Trailing zeros after a decimal point are significant (2.500 has 4 sig figs). Trailing zeros in a whole number without a decimal point are ambiguous but often considered not significant.
How to Round to Significant Figures
To round a number to N significant figures: start counting from the first non-zero digit, keep N digits, and round the last one based on the next digit. For example, rounding 0.004572 to 3 sig figs gives 0.00457. Rounding 12,345 to 3 sig figs gives 12,300.
Common questions
Are trailing zeros significant?
Trailing zeros after a decimal point are always significant (2.50 has 3 sig figs). Trailing zeros in a whole number without a decimal are ambiguous, 1200 might have 2, 3, or 4 sig figs depending on context. Using scientific notation removes ambiguity.
Why are significant figures important?
Significant figures indicate the precision of a measurement. Reporting more sig figs than your instrument can measure implies false precision. In calculations, the result should not have more sig figs than the least precise input.
How do exact numbers affect sig figs?
Exact numbers (like counting 12 eggs or conversion factors like 1 foot = 12 inches) have infinite significant figures. They do not limit the sig figs in a calculation result.
Counting rules follow standard conventions. Trailing zeros in a whole number with no decimal point are treated as not significant; write the number in scientific notation when you need to state precision exactly.