Significant Figures Calculator (Count and Round)
Type the number exactly as written (keep trailing zeros) and choose how many significant figures to round to.
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Significant Figures Calculator (Count and Round) by TheCalcTools
How the Significant Figures Calculator (Count and Round) works
Rules: all non-zero digits count; zeros between them count; leading zeros never count; trailing zeros count only if there is a decimal point. So 0.004050 has 4 significant figures, 1200 has 2, and 1200. has 4.
Scientific notation removes the ambiguity: 1.20 × 10³ clearly has 3 significant figures.
The formula
Worked example
Using the default values shown in the calculator:
| Number as written | 0.004050 |
|---|---|
| Round to significant figures | 2 |
- 0.004050 has 4 significant figures.
- Rounded to 2: 0.0041 = 4.1 × 10^-3.
Result:
| Significant figures in the number | 4 |
|---|---|
| Rounded | 0.0041 |
| Rounded, scientific notation | 4.1 × 10^-3 |
Frequently asked questions
How many significant figures in 1200?
Two by the usual convention, because trailing zeros without a decimal point are ambiguous. Write 1.200 × 10³ to show four.
Do exact numbers limit significant figures?
No. Counted or defined values (12 eggs, 100 cm in a metre) have unlimited significant figures.
Sources and further reading
- Wikipedia: Significant figures
- NIST SP 811: Guide for the use of the SI, rounding of numbers (appendix B)
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.