Significant Figures
Count significant figures and round numbers to a chosen sig-fig count.
Formula
Count + round to N sig figs
How to use
- 1Enter the number.
- 2Enter the target number of significant figures.
- 3Read the sig-fig count, the rounded value and the scientific-notation form.
About this calculator
Significant figures are how science says how precisely something was measured: 12.0 cm claims more precision than 12. This tool counts the significant figures in any number and rounds it to however many you need, showing the result in both ordinary and scientific notation so you can report measurements honestly.
Formula explained
Counting rules: all non-zero digits are significant; zeros between non-zero digits are significant; leading zeros are never significant; trailing zeros after a decimal point are significant; trailing zeros in a whole number are ambiguous. Scientific notation resolves that ambiguity: 1.5 × 10³ is two sig figs, 1.500 × 10³ is four.
Worked example
0.001230 has four sig figs. Rounded to three it becomes 0.00123, or 1.23 × 10⁻³ in scientific notation. The leading zeros never entered the count.
Tips & notes
- Carry extra digits through intermediate steps and round only the final answer.
- Switch to scientific notation when trailing zeros in a whole number are ambiguous.
- Keep sig figs and decimal places distinct: multiplication uses one, addition the other.