Significant Figures Calculator - Count and Round Sig Figs
Significant Figures Calculator
Count the significant figures in a number, or round to any number of them
Counts the Zeros Correctly
Applies the standard rules for leading zeros, zeros between digits, and trailing zeros with or without a decimal point.
Exact Rounding
Rounds the digits of your text, not a floating-point value, so 1.005 to 3 s.f. is 1.01 and trailing zeros are kept (3.5 to 4 s.f. is 3.500).
Scientific Notation
Shows the number in scientific notation, which makes exactly which digits are significant unambiguous.
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The Rules of Significant Figures
Significant figures are the digits that carry real information about a measurement. Non-zero digits always count. Zeros between non-zero digits count (4007 has 4). Leading zeros never count (0.0025 has 2). Trailing zeros count only when the number has a decimal point (2.50 has 3, but 250 is usually read as 2).
A number such as 1200 is genuinely ambiguous: it could have 2, 3 or 4 significant figures. Scientific notation removes the doubt, since 1.2 × 10³, 1.20 × 10³ and 1.200 × 10³ say exactly how precise you are. Zero itself is counted as having one significant figure here.
Key Takeaways
- Exact: Half-up rounding on the digits, with no floating-point surprises.
- Flexible input: Accepts decimals, leading signs and scientific notation like 1.20e3.
- Localised: Spanish and French pages accept a decimal comma.