Significant Figures Calculator
Round a number to 1–15 significant figures and see its scientific notation and rounding place.
Content updated August 1, 2026
Exact halfway cases round away from zero. The scientific-notation line makes significant trailing zeroes explicit when a whole-number display could otherwise be ambiguous.
Significant figures describe the digits that carry a number's stated precision, beginning with its first non-zero digit. Unlike decimal places, the significant-figure position moves with the size of the number.
Enter any finite number and choose 1 through 15 significant figures. The calculator shows the rounded value, scientific notation, numeric difference, and power-of-ten place where rounding occurred.
The Significant Figures formula
p = floor(log₁₀|x|) − s + 1; result = round(x ÷ 10^p) × 10^px = original non-zero number · s = requested significant figures · p = power-of-ten rounding place. Zero remains zero.
Worked example
For 12,345 rounded to three significant figures, p = 4 − 3 + 1 = 2. Rounding at 10² gives 12,300, written unambiguously as 1.23e+4.
Assumptions, rounding, and limitations
Assumptions
- The first non-zero digit begins the significant-figure count.
- Trailing decimal zeroes represent stated precision.
- Exact halfway cases round away from zero.
Rounding: Calculations keep the available floating-point precision; output is formatted to show the requested significant digits where decimal notation permits.
Limitations
- Supports 1 through 15 significant figures, matching the practical precision available in JavaScript numbers.
- Does not infer measurement uncertainty or decide how many significant figures a real-world measurement should report.
Sources
- NIST Guide to the SI, Chapter 7 — Expressing Values of Quantities — U.S. National Institute of Standards and Technology
Counting significant figures
Leading zeroes only locate the decimal point, so 0.0046 has two significant figures. Zeroes between non-zero digits are significant. Trailing decimal zeroes also communicate precision, which is why 1.200 represents four significant figures.
Trailing zeroes in a whole number can look ambiguous. The scientific-notation result removes that ambiguity: 12,300 to three significant figures is written 1.23e+4.
Frequently asked questions
▶Are leading zeroes significant?
No. In 0.00460, the zeroes before 4 locate the decimal point, while the final zero is significant; the number has three significant figures.
▶How is this different from decimal-place rounding?
Decimal places count positions after the decimal point. Significant figures count meaningful digits starting at the first non-zero digit, wherever it appears.
▶How are exact halfway cases rounded?
This calculator rounds exact halfway cases away from zero, so 9.95 to two significant figures becomes 10 and −9.95 becomes −10.
▶Why show scientific notation?
Scientific notation makes the intended significant trailing zeroes explicit, especially for large whole numbers and very small decimals.
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Open calculator →Disclaimer: Significant Figures Calculator results are estimates for general information and education only, and are not financial, tax, legal or medical advice. Verify important decisions with a qualified professional.