Significant Figures Calculator

Find how many significant figures a number has, see which digits count, round to any number of sig figs, and do arithmetic with the correct sig fig rules.

The rules for significant figures

Significant figures (sig figs) are the digits in a measured number that carry real information about its precision. Five rules decide which digits count:

Non-zero digits are always significant. 482 has 3 sig figs.
Zeros between non-zero digits are significant. 505 and 7.009 have 3 and 4.
Leading zeros are never significant. They only hold the decimal place: 0.0045 has 2.
Trailing zeros after a decimal point are significant. 3.20 has 3, and 100.0 has 4.
Trailing zeros in a whole number with no decimal point are ambiguous. 1200 could have 2, 3 or 4. Most classes count them as not significant, so 1200 has 2. Write 1200. or 1.200 × 10³ to show all four.

Number	Sig figs	Why
0.004050	4	Leading zeros don’t count; the final zero after the decimal does
1200	2	Trailing zeros with no decimal point are not counted
1200.	4	The decimal point makes the trailing zeros significant
100.0	4	Zeros between non-zero digits and after the decimal count
6.02 × 10²³	3	In scientific notation, every digit of the coefficient counts

Exact numbers, such as counted objects (12 students) or defined values (1 foot = 12 inches), have unlimited significant figures and never limit the precision of an answer.

Rounding to significant figures

Count from the first non-zero digit, keep the number of digits you need, and look at the next digit. If it is 5 or more, round up; otherwise leave the last kept digit alone. Rounding 0.0045678 to 2 sig figs gives 0.0046, and rounding 1234.5 to 3 sig figs gives 1230, which is clearer as 1.23 × 10³. Some teachers use “round half to even” for a 5 followed by nothing, so check which rule your class uses.

Significant figures in calculations

Multiplying and dividing: the answer has as many significant figures as the input with the fewest. 3.0 × 4.56 = 13.68, but 3.0 has only 2 sig figs, so the answer is 14.

Adding and subtracting: the answer is rounded to the least precise decimal place, not the fewest sig figs. 12.11 + 18.0 = 30.11, but 18.0 is only precise to the tenths place, so the answer is 30.1.

In multi-step problems, keep extra digits in the middle steps and round only the final answer. Rounding at every step can shift the last digit.

Frequently asked questions

How many significant figures does 0 have?

A lone zero is usually treated as having one significant figure. Measured zeros written with decimals, such as 0.00, are handled differently by different textbooks, so follow your class convention.

Do significant figures matter in math class?

Mostly in science. Chemistry and physics use them to show how precise a measurement is; pure math problems usually give exact answers instead.

Why do I get an answer in scientific notation?

When a rounded answer ends in zeros, like 1230 to 3 sig figs, the plain form would look like it has fewer sig figs than it does. Scientific notation, 1.23 × 10³, removes the doubt. The scientific notation calculator converts between the two.

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Last updated September 27, 2026.