Significant Figures (count + round)
Count sig figs in a number; round to a target N.
Example
You enter
- Number (decimal or scientific) 0.00347
- Round to N sig figs (optional) 2
You get
- Significant figures in input 3
- Rounded to target sig figs 0.0035
Checked against published worked examples from: NIST SP 811 §7 (public); NIST.
Details, formula, and sources
ScopeLeading zeros not significant; trailing zeros after a decimal ARE.
Formula or tableSig-fig count: non-zero digits are always significant; zeros between non-zeros are significant; leading zeros are not; trailing zeros after a decimal point ARE significant. Trailing zeros in a bare integer are ambiguous and NOT counted here (use scientific notation for explicit precision). Rounding to N sig figs follows NIST SP 811 B.7.1 on the number's decimal digits: a dropped digit below 5 truncates, a dropped 5 followed by any nonzero digit rounds up, and a dropped 5 followed only by zeros rounds to the even digit.
Source and editionSignificant-figure conventions per NIST SP 811 §7 (Guide for the Use of the International System of Units).
Free accessFree at nist.gov/pml/special-publication-811.
What governsEstimate only. Readability formulas and similar metrics are derived from a representative population and have known edge-case noise. The classroom teacher governs final text selection, grade placement, and assessment decisions.
API field namesvalue, target_sig_figs, input_sig_figs, rounded_value
- Bare-integer trailing zeros not counted; use scientific notation (1.500e3) or a trailing decimal (1500.) to mark them as significantconvention; the rule is ambiguous in plain decimal
- Rounding mode round half to even on the decimal digits (a 5 followed only by zeros)NIST SP 811 B.7.1 rule 3