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Significant figures rules — which zeros count and which don't — trip up even careful students, especially with leading and trailing zeros around a decimal point. This calculator counts the significant figures in any number and can round it to a specific number of sig figs, with a full step-by-step solution.
How it works
Enter a number as you'd normally write it (including any trailing zeros and decimal point). The calculator applies the standard significant figures rules: all non-zero digits count, zeros between non-zero digits count, leading zeros never count, and trailing zeros count only when a decimal point is present.
- Enter number.
- Enter round to N significant figures (optional).
- Click Calculate to see your results.
Examples
Counting 0.004500
0.004500 has 4 significant figures (4, 5, 0, 0) — the leading zeros before the "4" don't count, but the trailing zeros after it do, since there's a decimal point.
Who should use it
- Checking significant figures for a chemistry or physics lab report.
- Rounding a measured value to an appropriate number of significant figures before reporting it.
Industry applications
- Chemistry and physics education
- Scientific measurement and lab reporting
Advantages
- Applies the standard significant figures counting rules precisely, including edge cases with leading/trailing zeros.
- Can also round a number to a specified number of significant figures.
Limitations
- Uses the common textbook trailing-zero convention for numbers without a decimal point, which is not universally standardized without additional notation.
Common mistakes to avoid
- Assuming trailing zeros without a decimal point are always significant — by the common textbook convention, they aren't, unless the number is written with a decimal point or explicit notation.
- Counting leading zeros as significant, which they never are.
Best practices
- When precision matters and a number has ambiguous trailing zeros, write it with an explicit decimal point (like "1500." or "1.500 × 10³") to remove any doubt about which digits are significant.
Tips
- When multiplying or dividing measured values, the result should be reported with the same number of significant figures as the least-precise input value.