Note that the rule is about decimal places, not the count of sig figs.
How the sig fig calculator works
SigFigCalc reads your number as text, not as a floating-point value, so it never loses trailing zeros or picks up computer rounding errors. It finds the first non-zero digit, then decides how far the significant digits run: to the very last digit if there is a decimal point, or to the last non-zero digit if there is not. Any zeros after that in a whole number are marked as ambiguous.
Examples
| Number | Sig figs | Why |
|---|---|---|
| 4,507 | 4 | The zero is between non-zero digits |
| 0.0450 | 3 | Leading zeros do not count; the trailing zero does |
| 1200 | 2 (up to 4) | Trailing zeros without a decimal point are ambiguous |
| 1200. | 4 | The decimal point makes the zeros significant |
| 6.022 × 10²³ | 4 | Only the digits before the power of ten count |
Calculations
Sums and differences are rounded to the least precise decimal place among the inputs. Products and quotients are rounded to the fewest significant figures among the inputs. SigFigCalc computes the exact answer first with big-number decimal arithmetic, then rounds once, half away from zero. For long problems, keep all digits until the final step. Everything is calculated in your browser.
Frequently asked questions
What is the sig fig rule for addition?
Round to the fewest decimal places among the numbers.
What is 5.0 − 2.25 with sig figs?
2.75 rounds to 2.8.
Can the answer have more sig figs than the inputs?
Yes. 9.5 + 0.7 = 10.2 has three.
Is SigFigCalc free?
Yes, with no sign-up or ads.
Are my numbers saved?
Yes, in this browser only.