Significant Figures Calculator
Count the significant figures in a number and round it to a chosen number of significant figures.
About the Significant Figures Calculator
Type a number as written (decimals, whole numbers or scientific notation such as 6.02e23) and choose how many significant figures to round to. The calculator counts the significant figures and gives the rounded value in ordinary and scientific notation.
Rules: all non-zero digits count; zeros between them count; leading zeros never count; trailing zeros count only if there's a decimal point. So 0.004520 has 4, 1200 has 2 (ambiguous) and 1200. has 4.
The formula
Round to n s.f.: keep n digits from the first non-zero digit
Worked example
0.004520
- Leading zeros don't count; the final zero after the decimal point does
- 4 significant figures (4, 5, 2, 0)
- Rounded to 2: 0.0045 (4.5 × 10⁻³)
Questions people ask
How many sig figs in a product?
Use the fewest significant figures among the inputs.
And in a sum?
Use the fewest decimal places among the inputs.
Do exact numbers limit sig figs?
No: counted numbers and defined constants (12 in a dozen) have unlimited precision.