Significant Figures Calculator
Count the significant figures in a number as you wrote it, and round any number to up to 40 significant figures.
Every nonzero digit is significant, zeros between them are significant, leading zeros never are, and trailing zeros count only when the number has a decimal point. So 0.00250 has 3 significant figures and 1002 has 4. Rounded to 3 significant figures, 0.028675 becomes 0.0287.
The calculator follows the counting and rounding rules in OpenStax Chemistry 2e, including rounding a lone 5 to the even digit. Some textbooks and teachers always round 5 up, or count trailing zeros in whole numbers differently, so check the convention your course or lab uses. It counts zero itself as having no significant figures by these rules and does not apply the rules for adding or multiplying measurements.
Significant figures in 0.028675
5
- Rounded to 3 significant figures
- 0.0287
- Scientific notation
- 2.87 × 10^-2
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About the Significant Figures Calculator
Significant figures are the digits in a measurement that carry real information, and zeros are the only digits that need thought. A zero between other digits is significant, so 1002 has 4. Zeros at the front only place the decimal point, so 0.00250 has 3: the 2, the 5 and the final 0, which counts because it was written after the decimal point. Zeros at the end of a whole number are the hard case. Written as 1300, the number could have 2, 3 or 4 significant figures, and the cautious reading is 2. Scientific notation removes the doubt: 1.3 x 10^3 has 2, 1.30 x 10^3 has 3. Rounding drops digits from the right. A dropped digit below 5 leaves the last kept digit alone and above 5 raises it, so 18.3384 to three figures is 18.3 and 6.8752 is 6.88. A dropped 5 followed by any nonzero digit rounds up; a dropped 5 with nothing after it rounds to the even digit, so 92.85 becomes 92.8. When the rounded answer ends in zeros left of the decimal point, as 1300 rounded to 3 figures does, the calculator also shows 1.30 x 10^3.
Frequently asked questions
How many significant figures does 1300 have?+
It is ambiguous: 2, 3 or 4, because the trailing zeros might only hold places. The cautious reading is 2. Write 1.3 x 10^3 for 2 figures, 1.30 x 10^3 for 3, or 1.300 x 10^3 for 4.
Are zeros significant?+
Zeros between nonzero digits always are, as in 1002. Leading zeros never are, as in 0.00250. Trailing zeros are significant when the number has a decimal point, so 2.50 has 3, but not reliably in a whole number such as 1300.
How do you round to significant figures?+
Count from the first nonzero digit, keep that many digits, and look at the first one you drop. Below 5, round down; above 5, round up; a 5 followed by other nonzero digits rounds up. 0.028675 to three figures is 0.0287.
Why does 92.85 round down to 92.8?+
When the dropped digit is exactly 5 with nothing after it, the rule some chemistry courses teach rounds to the even digit. 8 is even, so 92.85 becomes 92.8. Some classes always round a 5 up instead; check which rule your course uses.
Counting and rounding rules and the worked examples: OpenStax, Chemistry 2e, section 1.5.
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