Education
Sig Fig Calculator
Type the number exactly as you would write it on paper. The calculator counts the significant figures, applies the standard rules for leading and trailing zeros, and rounds to your chosen sig fig target.
Number
Type the number exactly as written, including any trailing or leading zeros. The trailing-zero rule depends on whether a decimal point is shown, so write 1500. or 1.500 × 10³ to make a zero significant.
e.g. 0.00450
At least 1. · e.g. 2
Rules in plain English
- All nonzero digits are significant.
- Zeros between nonzero digits are significant.
- Leading zeros (before the first nonzero digit) are never significant.
- Trailing zeros are significant only if a decimal point is shown.
- Scientific notation makes the count unambiguous.
All digits from the first nonzero digit to the end of the number are significant (the trailing zeros count because the decimal point is shown).
Significant figures
3
Rounded to 2 sig figs: 0.0045
For arithmetic with mixed precision, the result inherits the smaller sig fig count. For rounding to decimal places instead, use the rounding calculator.
Examples
0.00450
3 sig figs
1,000
1 sig fig (no decimal shown)
1,000.
4 sig figs (explicit decimal point)
Round 3.14159 to 3 sig figs
= 3.14
How it works
Significant figure counting is a rule-based scan from the first nonzero digit. Leading zeros never count; embedded zeros always count; trailing zeros count only when the number shows a decimal point or is written in scientific notation.
Rounding · round to step = 10⌊log₁₀|x|⌋ − k + 1
k is the target sig fig count. The step is the power of 10 just below the last digit kept.
Related precision calculators
- Rounding calculator for rounding to decimal places or to nearest whole/ten/hundred/thousand.
- Scientific notation calculator for an unambiguous way to write very large and very small numbers.
- Scientific calculator for the arithmetic that produced your measurement.
- All education calculators.
Frequently asked questions
Significant figures are the digits in a number that carry actual measurement precision. Counting them tells you how reliable a value is. 12.30 has four sig figs; 0.0045 has two; 1500 has two unless a decimal point or scientific notation says otherwise.
In a whole number like 1500, the trailing zeros could be precise or could be placeholders. Writing 1500. with an explicit decimal point, or 1.500 × 10³ in scientific notation, removes the ambiguity and counts them as significant.
Locate the first sig fig, count over to your target, and look at the next digit. Round half-up away from zero. The calculator does this and shows both the rounded decimal and its scientific notation form.
By common convention, 0 is counted as 1 significant figure. It is also fine to treat it as undefined for sig fig purposes; the calculator picks the practical convention.
For multiplication and division, the result keeps as many sig figs as the input with the fewest. For addition and subtraction, the result keeps as many decimal places as the input with the fewest. The sig fig calculator does not do operation chaining; it counts and rounds a single value.
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