Significant Figures Calculator
Round a number to a chosen number of significant figures.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Significant figures express the precision of a measurement. Scientific work reports results to the number of significant figures justified by the least precise input, rather than to a fixed number of decimal places.
Worked example
calculated with the default values below
Number 0.00456789 · Significant figures 3 Rounded value 0.0045700000 · Order of magnitude -3 · Scientific notation 4.57e-3 · Decimal places needed 5
General background references
Disclaimer
These calculators give general mathematical results. They suit study, planning and estimation — verify anything that feeds a graded submission, a published figure or a financial commitment.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
e = ⌊log₁₀|v|⌋; r = round(v×10^(n−1−e))÷10^(n−1−e)
- v
- Input value
- n
- Significant figures
- e
- Order of magnitude
- r
- Rounded value
Scientific notation v ≈ r×10^e; decimal places = max(n−1−e, 0); for v = 0 every result is 0.
Frequently asked questions
Why do leading zeros not count toward the significant figures?
Only digits that carry measurement information matter. For 0.00456789 the first three significant figures are 4, 5 and 6, so rounding to three significant figures gives 0.00457, and the three zeros after the decimal are placeholders showing position, not precision. The tool derives the exponent from log10 and keeps figures minus one minus that exponent decimal places, which drops those leading zeros automatically rather than counting them.