Significant Figures Calculator — Count & Round Sig Figs
Paste any number to instantly count its significant figures and see a step-by-step breakdown of which digits are significant and why. Then round it to any number of sig figs.
Significant figures in "0.004560"
|x| = 0.00456, magnitude = floor(log₁₀(0.00456))
Rounding unit = 10^(magnitude − n + 1) = 10^(-3 − 3 + 1)
Rounded value to 3 sig figs
- 1
Magnitude m = ⌊log₁₀|x|⌋
⌊log₁₀(0.00456)⌋ = -3 - 2
Rounding unit = 10^(m − n + 1)
10^(-3 − 3 + 1) = 0.00001The place value to round to: determines how many sig figs survive. - 3
Rounded = round(x ÷ unit) × unit
round(0.00456 ÷ 0.00001) × 0.00001 = 0.00456
How does this calculator work?
Significant figures count the reliably known digits in a number: non-zero digits always count; zeros between non-zero digits count; leading zeros do not; trailing zeros after a decimal point do; trailing zeros in integers are ambiguous. To round to n sig figs: rounded = round(x / 10^(m−n+1)) × 10^(m−n+1) where m = ⌊log₁₀|x|⌋.
Formula
How this is calculated
Significant figures communicate measurement precision — how many digits in a value are reliably known. The counting rules are: (1) all non-zero digits are always significant; (2) zeros sandwiched between non-zero digits ("captive" zeros) are significant; (3) leading zeros (before the first non-zero digit, e.g. the three zeros in 0.00456) are not significant — they just position the decimal; (4) trailing zeros after a decimal point are significant (0.500 has three sig figs); (5) trailing zeros in a whole number with no decimal point are ambiguous — 1200 could have 2, 3 or 4 sig figs depending on the measurement, which is why scientific notation or an explicit decimal point (1200.) is preferred.
To round to n significant figures: find the magnitude m = ⌊log₁₀|x|⌋, compute the rounding unit u = 10^(m−n+1), then evaluate round(x/u) × u. For example, to round 0.004560 to 2 sig figs: m = −3, u = 10^(−3−2+1) = 10^(−4) = 0.0001, round(0.004560/0.0001) × 0.0001 = round(45.6) × 0.0001 = 46 × 0.0001 = 0.0046.
The step-by-step breakdown below traces both the counting and rounding so you can follow the reasoning for any input.
Frequently asked questions
It is ambiguous. 1200 could have 2 sig figs (only 1 and 2 are known), 3 (the trailing zero after 2 is significant), or 4 (all four digits are significant). To remove ambiguity, write 1.2 × 10³ (2 sig figs), 1.20 × 10³ (3 sig figs), or 1.200 × 10³ (4 sig figs). This calculator conservatively treats trailing zeros in integers as non-significant.
The three leading zeros (0.00) are not significant — they are placeholders needed to locate the decimal point. The significant digits are 4, 5, 6, and the trailing 0 (which is significant because it appears after the decimal point and signals that the measurement is precise to that place value). So: 4 sig figs.
In science and engineering, the number of sig figs in a result should not exceed the precision of the least-precise measurement used. For multiplication and division, use the fewest sig figs of any factor. For addition and subtraction, align decimal places instead (use the rightmost decimal place of the least-precise addend).
Also known as
TG we-Calculate Editorial Team. (2026). Significant Figures Calculator — Count & Round Sig Figs [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/sig-fig-calculator
TG we-Calculate Editorial Team. "Significant Figures Calculator — Count & Round Sig Figs." TG we-Calculate. 2026. https://we-calculate.com/calculator/sig-fig-calculator.
TG we-Calculate Editorial Team, "Significant Figures Calculator — Count & Round Sig Figs," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/sig-fig-calculator
@misc{wecalculate_sig_fig_calculator, title = {Significant Figures Calculator — Count & Round Sig Figs}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/sig-fig-calculator}}, year = {2026}, note = {TG we-Calculate} }
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