Math · Significant figures
Sig fig arithmetic calculator.
Enter two or more measurements, choose add and subtract or multiply and divide, and get the answer rounded by the significant figure rule: fewest decimal places when adding or subtracting, fewest significant figures when multiplying or dividing. The unrounded value is computed exactly and rounded once at the end. Runs in your browser; nothing is sent.
12.11 + 18.0 + 1.013 = 31.123 before rounding. 18.0 has the fewest decimal places (one), so the answer is 31.1. For 4.56 × 1.4 = 6.384, 1.4 has the fewest significant figures (two), so the answer is 6.4.
Your measurements
Your answer
Fill the form and press Calculate.
The two rules
Multiplication and division: the answer has the same number of significant figures as the number with the fewest significant figures. Addition and subtraction: the answer has the same number of decimal places as the term with the fewest decimal places. The two rules look at different things, which is why 100.0 − 99.96 = 0.04 is rounded to 0.0 (one decimal place, from 100.0) and ends up with no significant figures worth quoting.
How this calculator applies them
It computes the unrounded result exactly from the digits you typed, finds the number that limits the answer, and rounds once at the end (rounding at each step compounds error). Ties round up. For multiplication and division it counts significant figures of each factor with the standard rules (leading zeros never count, trailing zeros count after a decimal point). A plain whole number such as 1400 is counted as having two significant figures, the lowest reading, and flagged as ambiguous. For addition and subtraction it counts decimal places, so 1400 has none and 1.4e3 has −2 (it is known to the hundreds). A number marked exact is ignored by the rule. This tool handles one kind of operation at a time; for mixed expressions such as (a + b) × c, do the steps one after another and keep an extra digit between them.
Worked examples
Add: 12.11 + 18.0 + 1.013 = 31.123. The decimal places are 2, 1 and 3; the fewest is 1, so the answer is 31.1. Multiply: 4.56 × 1.4 = 6.384. The sig figs are 3 and 2, so the answer has 2: 6.4. Divide: 6.50 ÷ 3.2 = 2.03125; the sig figs are 3 and 2, so the answer is 2.0. With an exact number: 2.5 × 4 where the 4 is a count gives 10, limited only by 2.5’s two significant figures and written 1.0 × 101. Whole number: 1400 + 2.25 = 1402.25, rounded to zero decimal places for 1402.
Sources, opened 8 October 2026: Chemistry LibreTexts, 2.4: Significant Figures in Calculations (the multiplication and division rule and the addition and subtraction rule); Chemistry LibreTexts, 2.3: Significant Figures - Writing Numbers to Reflect Precision (counting significant figures, and exact numbers having infinitely many).
Note: Educational calculator. Some courses carry guard digits, round half to even, or treat trailing zeros of whole numbers differently. Follow your instructor’s convention.
Frequently asked questions
How many significant figures should the answer of a multiplication have?
The same as the factor with the fewest significant figures. 4.56 x 1.4 = 6.384, and because 1.4 has two significant figures the answer is 6.4.
How do you round when adding or subtracting?
Round to the same number of decimal places as the term with the fewest decimal places. 12.11 + 18.0 + 1.013 = 31.123, and 18.0 has one decimal place, so the answer is 31.1.
Why are the rules different for adding and multiplying?
Adding combines absolute precision, which is set by the last decimal place of each term. Multiplying combines relative precision, which is set by how many significant digits each factor has.
Do exact numbers count?
No. Counted objects and defined values, such as 12 inches in a foot, have unlimited significant figures, so they never limit the answer. Tick the exact box for those numbers.
Should I round in the middle of a multi-step calculation?
It is better to keep extra digits through the steps and round once at the end, because rounding early compounds the error. This calculator computes the full value first and rounds only the final answer.
Does this calculator work with scientific notation?
Yes. Type numbers such as 6.02e23 or 1.50e-3. In scientific notation every digit before the exponent is significant, so 1.50e-3 has three significant figures.