Sig Fig Rules Calculator
Use this free sig fig rules calculator to count the significant figures in any number and see exactly which rules apply. Enter a number to get an instant breakdown of its significant digits with rule-by-rule explanations.
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Enter any number to analyze its significant figures
Result
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Formula
Significant figures are counted by applying a set of rules: all non-zero digits count, zeros between significant digits count, trailing zeros after a decimal count, and leading zeros never count.
Worked Example
The Rules for Counting Significant Figures
- Rule 1: All non-zero digits (1-9) are always significant
- Rule 2: Zeros between non-zero digits ("captive zeros") are always significant, e.g. 1005 has 4 sig figs
- Rule 3: Leading zeros are never significant. They are placeholders only, e.g. 0.0032 has 2 sig figs
- Rule 4: Trailing zeros after a decimal point are significant, e.g. 2.500 has 4 sig figs
- Rule 5: Trailing zeros in a whole number without a decimal are ambiguous, e.g. 1200 could be 2, 3, or 4 sig figs depending on context
When in doubt about trailing zeros in whole numbers, scientific notation removes all ambiguity. Writing 1.20 x 10^3 makes it clear there are 3 significant figures.
You can also calculate changes using our Sig Fig Rounding Calculator, Sig Fig Scientific Notation Calculator or Sig Fig Addition Calculator.
Frequently Asked Questions
How many significant figures does 100 have?
It is ambiguous. Without a decimal point, 100 could have 1, 2, or 3 sig figs depending on the precision of the measurement. Writing 100. (with a trailing decimal) indicates 3 sig figs. Writing 1.00 x 10^2 in scientific notation also makes it unambiguous.
Are trailing zeros significant?
It depends on position. Trailing zeros after a decimal point are always significant (e.g. 2.50 has 3 sig figs). Trailing zeros in a whole number without a decimal point are ambiguous (e.g. 300 might have 1, 2, or 3 sig figs).
How many sig figs does 0 have?
Zero by itself has 1 significant figure. However, 0.0 has 1 sig fig (the trailing zero after the decimal is significant but the leading zero is not).
What are captive zeros?
Captive zeros are zeros that appear between non-zero digits. They are always significant. For example, in 1.007 the two zeros are captive and all 4 digits are significant.
Why do significant figures matter?
They prevent you from claiming more precision than your measurements actually provide. In science, reporting a result with too many digits implies a level of accuracy your instruments may not support, which can lead to incorrect conclusions.
How do exact numbers affect sig figs?
Exact numbers (like counting 12 eggs or using the conversion 1 inch = 2.54 cm exactly) have unlimited significant figures and never limit the precision of a calculation.
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