Type any number — including scientific notation like 5.20e-3 — and see how many significant figures it has, with every digit color-coded and each rule explained. Then round any number to 1–10 sig figs in plain and scientific notation.
• 3 leading zeros (before the first nonzero digit) are not significant — they only mark the decimal place.
• 1 trailing zero is significant because the number has a decimal point.
Round to significant figures
Rounded to 3 sig figs
3.14
Scientific notation
3.14 × 100
📌 In the plain-notation result, extra zeros added to reach the decimal point are placeholders, not significant digits — scientific notation is the unambiguous form.
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The 5 rules of significant figures
Rule
Example
Sig figs
1. Nonzero digits are always significant
234.5
4
2. Zeros between nonzero digits (captive zeros) are significant
4,005
4
3. Leading zeros are never significant
0.00520
3
4. Trailing zeros are significant only when the number has a decimal point
25.00
4
5. Trailing zeros without a decimal point are ambiguous — assumed not significant
4,500
2
Worked example: 0.00520
Take 0.00520. The three zeros at the front are leading zeros — they appear before the first nonzero digit and only position the decimal point, so they do not count. The 5 and 2 are nonzero digits and always count. The final 0 is a trailing zero in a number that has a decimal point, so it counts too. Result: 3 significant figures — which is exactly why a scientist writes 0.00520 instead of 0.0052: the extra zero deliberately claims one more digit of measured precision. In scientific notation the same number is 5.20 × 10⁻³, where all three digits of the mantissa are visibly significant.
Rounding works from the left: to round 0.0052047 to 3 sig figs, keep the first three significant digits (5, 2, 0), look at the next digit (4, less than 5) and round down: 0.00520.
Frequently asked questions
Written as plain "100" it is ambiguous — by the standard convention only the 1 counts, so 100 has 1 significant figure. Writing "100." (with a decimal point) makes it 3, and scientific notation removes all doubt: 1 × 10² is 1 sig fig, 1.0 × 10² is 2, and 1.00 × 10² is 3.
One. The zeros in 0.005 are all leading zeros — they come before the first nonzero digit and only mark the decimal place, so they are never significant. Only the 5 counts. By contrast, 0.0050 has 2 sig figs because its final trailing zero comes after the decimal point.
Sig figs communicate measurement precision. A balance reading of 2.50 g claims precision to the hundredth of a gram; writing 2.5 g would claim less. Reporting a result with more sig figs than your least precise measurement invents precision you never had, which is why chemistry classes grade sig figs as strictly as the numeric answer.
For multiplication and division, the result keeps as many significant figures as the input with the fewest sig figs: 2.5 × 3.42 = 8.55 rounds to 8.6 (2 sig figs). For addition and subtraction, the result keeps the fewest decimal places instead: 12.11 + 0.3 = 12.41 rounds to 12.4 (one decimal place, because 0.3 has only one).
Yes — zeros sandwiched between nonzero digits (captive zeros) are always significant. 4,005 has 4 significant figures and 1.02 has 3. Only leading zeros (0.005) and trailing zeros without a decimal point (4,500) fail to count.
Cite this calculator
APACalcBrew. (2026). Sig Fig Calculator. https://calcbrew.com/sig-fig-calculator