Significant figures calculator
Count the sig figs in any number, see exactly which rule applies, and round to the precision your answer needs.
The rules for significant figures
- Nonzero digits are always significant: 452 has 3.
- Zeros between nonzero digits are significant: 1002 has 4.
- Leading zeros are never significant: 0.0045 has 2.
- Trailing zeros after a decimal point are significant: 4.500 has 4.
- Trailing zeros in a whole number with no decimal point are ambiguous: 1200 has 2 by most conventions, while 1200. has 4.
- In scientific notation, count only the digits in the coefficient: 3.00 × 10⁸ has 3.
Sig figs in calculations
Multiplying and dividing: round the answer to the fewest significant figures among the inputs. 4.56 × 1.4 = 6.384 → 6.4 (2 sig figs).
Adding and subtracting: round to the fewest decimal places. 12.11 + 18.0 + 1.013 = 31.123 → 31.1 (one decimal place).
Keep extra digits during intermediate steps and round only the final answer, so rounding errors don’t pile up.
How rounding works here
The calculator rounds half up, the rule taught in most classes: 2.675 to 3 sig figs is 2.68. It works on the digits you type instead of converting to binary, so it never shows the floating-point errors some calculators do.
When to use scientific notation
If rounding leaves placeholder zeros, scientific notation is the only unambiguous way to write the answer. Rounding 999.7 to 3 sig figs gives 1.00 × 10³. Written as 1000, a reader can’t tell how many zeros were measured.
Common questions.
How many significant figures does 100 have?
One, by the usual convention, because trailing zeros in a whole number without a decimal point are treated as placeholders. Written as 100. it has 3, and 1.00 × 10² also has 3.
Are exact numbers limited by sig figs?
No. Counted values (12 eggs) and defined constants (1 m = 100 cm) have unlimited significant figures and never limit the precision of your answer.
How many sig figs does 0.0 have?
A measured zero like 0.0 is a special case. Most teachers count the zeros after the decimal point, so 0.0 has 1 and 0.00 has 2.
Does the calculator handle scientific notation?
Yes. Type 6.022e23, 6.022×10^23, or 6.022 x 10^23. Only the coefficient’s digits count.