Math

Significant Figures Calculator

Round any number to a specified count of significant figures. Enter your number and sig fig count for an instant, correctly formatted result.

Enter a number and the desired significant figures count.

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How Sig Fig Rounding Works

To round to n significant figures, locate the nth significant digit and round based on the digit that follows it.

Round = n.toPrecision(sigFigs)

Examples:

123456 → 3 sig figs → 123000

0.008475 → 2 sig figs → 0.0085

9.9994 → 4 sig figs → 9.999

Sig Figs in Scientific Measurement

In experimental science, every measurement carries some uncertainty. A ruler marked in millimetres can measure to the nearest millimetre, so reporting a length as 14.372 cm suggests a false level of precision. Significant figures communicate the actual precision of a measurement by indicating which digits are reliable.

Calculators and computers carry many decimal places internally, but those extra digits do not represent real measurement precision. The significant figures convention is a discipline of honest reporting — you state only what you actually know. A result of 12.5 g implies the measurement is reliable to the nearest 0.1 g, while 12 g implies reliability only to the nearest gram.

Exact numbers — counting numbers like "5 apples" or defined constants like "1 km = 1000 m" — have infinite significant figures and do not limit the precision of your calculations. Only measured quantities carry precision limitations that propagate through arithmetic.

Frequently asked questions

What are significant figures?
Significant figures (also called significant digits) are the meaningful digits in a number that carry information about the precision of a measurement. All non-zero digits are significant. Zeros between non-zero digits are significant. Leading zeros (before the first non-zero digit) are not significant. Trailing zeros after a decimal point are significant. For example, 0.00453 has three significant figures (4, 5, and 3); the leading zeros are not significant.
How do you round to significant figures?
To round a number to n significant figures: identify the first significant digit, count n digits from there, and look at the digit immediately after the nth. If it is 5 or more, round up the nth digit; if it is less than 5, leave the nth digit unchanged and drop subsequent digits. For example, rounding 0.008475 to 3 significant figures gives 0.00848 (the fourth significant digit, 7, rounds up the 4 to 5, but 5 stays as 5 because the next digit 7 ≥ 5 means the 4 becomes 5). Wait — 0.00847|5: third sig fig is 7, next digit is 5 so 7 rounds to 8, giving 0.00848.
Why do significant figures matter in science?
Significant figures convey the precision of a measurement or calculation result. Reporting more significant figures than your measuring instrument can resolve is misleading; reporting fewer loses information. In multi-step calculations, rounding errors can accumulate. The convention is to keep at least one extra significant figure during intermediate steps and round to the appropriate number only in the final answer. Scientific papers and engineering specifications always state the precision of measurements using significant figures.
What is the difference between significant figures and decimal places?
Decimal places count the number of digits after the decimal point regardless of value. Significant figures count the meaningful digits in the number regardless of where the decimal point is. For the number 0.00456, it has 3 significant figures but 5 decimal places. For the number 1200, it has 2, 3, or 4 significant figures depending on context, but 0 decimal places. Significant figures are a measure of precision in terms of relative magnitude, while decimal places measure precision in terms of absolute magnitude.
How do significant figures work in multiplication and division?
When multiplying or dividing, the result should have the same number of significant figures as the measurement with the fewest significant figures. For example, 3.47 × 2.1 = 7.287 rounded to 7.3 (two significant figures, because 2.1 has only two). This rule ensures that the precision of your result does not exceed the precision of your least precise input. The idea is that your answer can only be as precise as your weakest measurement.
How do significant figures work in addition and subtraction?
When adding or subtracting, the result should have the same number of decimal places as the number with the fewest decimal places. For example, 12.456 + 0.01 = 12.466 rounded to 12.47 (two decimal places, matching 0.01). This differs from the multiplication rule because addition and subtraction depend on absolute precision (how many decimal places), not relative precision (how many significant figures). Always apply the correct rule based on whether you are multiplying/dividing or adding/subtracting.

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