Significant Figures Converter
Free, with no sign up. Rounding runs in your browser and uses decimal-string arithmetic, so binary floating-point does not change a half-up tie. Exponent notation is supported.
Your result
Formula: keep the requested significant digits; if the next digit is 5 or greater, increase the last kept digit.
Worked example
12.345 to 4 significant figures rounds to 12.35. 9.99 to 2 rounds to 10. (scientific notation: 1.0 × 10^1), making the two significant digits visible.
Leading zeros never count. Zeros after a decimal point following a nonzero digit count; trailing zeros in a whole number without a decimal point are treated as not significant, so 1250 has 3 and is flagged as ambiguous. A decimal point makes them significant: 100. has 3. Results include both plain and scientific notation.
How it works
The rounding step operates on decimal digits and applies half-up rounding exactly.
How to use this tool
Use the fields below and select the action button to calculate.
Frequently asked questions
What rounding rule does this use?
Exact decimal half-up: when the first discarded digit is 5 or greater, the final retained digit increases.
When are trailing zeros significant?
Zeros after a decimal point and after a nonzero digit count; trailing zeros in an integer without a decimal point do not. For example, 1.20 has three significant figures, while 1250 has three.
Does this upload my number?
No. The calculation runs in your browser; your input stays on this device.