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Significant Figures Calculator

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Count the significant figures in a number, or round a number to a specific number of significant figures.

Significant Figures Calculator

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Significant figures
4
A trailing zero with no decimal point (like "1200") is ambiguous - write it as "1200." or in scientific notation to specify precision exactly.

The rules

All non-zero digits are significant Zeros between non-zero digits are significant (e.g., 105 -> 3 sig figs) Leading zeros are never significant (e.g., 0.0052 -> 2 sig figs) Trailing zeros are significant only if there's a decimal point (e.g., 3.140 -> 4, but 3140 -> ambiguous)
Example

0.004520 has 4 significant figures - the leading zeros don't count, but the trailing zero after the decimal point does.

Step-by-step guide

  1. Enter a number - as typed, including any decimal point.
  2. Read the significant figure count.
  3. Optionally enter a target sig fig count to see the number rounded appropriately.

Why significant figures matter in science

Significant figures communicate the precision of a measurement - reporting a result as "5.2 cm" versus "5.20 cm" isn't just stylistic, it implies a genuinely different level of measurement precision (the second suggests confidence down to the hundredths place). In calculations built from measured values, a result can't honestly claim more precision than its least precise input, which is why scientific calculations follow specific sig fig rules when multiplying, dividing, adding, or rounding results.

Common mistakes

Counting leading zeros as significant - "0.0052" has only 2 significant figures, since zeros before the first non-zero digit are never significant.
Assuming trailing zeros without a decimal point are always significant - "1200" is genuinely ambiguous (could be 2, 3, or 4 sig figs) unless written with a decimal point or in scientific notation.

Frequently asked questions

How many sig figs does "1200" have?

It's genuinely ambiguous without more context - it could be 2, 3, or 4 significant figures depending on the actual measurement precision. Writing it as "1200." (with a trailing decimal point) or in scientific notation (1.200 x 10³ for 4 sig figs) removes the ambiguity.

Are exact numbers (like counting 5 apples) subject to sig fig rules?

No - counted, exact quantities and defined constants are treated as having infinite significant figures, since there's no measurement uncertainty involved. Sig fig rules apply specifically to measured values.

Do sig fig rules differ for addition versus multiplication?

Yes - multiplication and division results are limited by the factor with the fewest significant figures, while addition and subtraction results are limited by the least precise decimal place among the values, a different rule entirely.

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