Round to Significant Figures Calculator
Rounding to significant figures keeps a fixed number of meaningful digits in a value, controlling its relative precision rather than the number of decimal places. It is the way scientists and engineers report measurements so the precision is clear and not overstated. This tool rounds any number to the count of significant figures you choose, using the everyday round-half-away-from-zero rule, and reports both the ordinary rounded value and the unambiguous scientific-notation form. It also shows the order of magnitude so you can see the scale of the number at a glance.
Significant figure rounding formula
Order of magnitude d = floor(log10(|x|))
Scale factor = 10^(n - 1 - d)
Rounded value = round(x * scale factor) / scale factor
Here x is your number and n is the requested number of significant figures. The order of magnitude locates the leading digit, and the scale factor shifts the rounding boundary to the nth significant place.
How significant figure rounding works
- Significant figures count from the first nonzero digit through the last digit kept.
- Leading zeros are never significant; they only set the scale of the number.
- Rounding to significant figures controls relative, not absolute, precision.
- This tool uses round-half-away-from-zero, the common everyday convention.
- Scientific notation makes the kept number of significant figures unambiguous.
Significant figures: frequently asked questions
What are significant figures?
Significant figures are the digits in a number that carry meaningful information about its precision. They start from the first nonzero digit and run through to the last digit kept. The number 0.004560 has four significant figures: 4, 5, 6 and the trailing zero, while leading zeros are not significant.
How does rounding to significant figures work?
To round to n significant figures, you keep the first n significant digits and round the rest. For example 3,141.59 to three significant figures is 3,140, and to two significant figures is 3,100. Rounding to significant figures controls relative precision, unlike rounding to decimal places which controls absolute precision.
What rounding rule does this calculator use?
This calculator uses round-half-away-from-zero, the most common everyday convention, where a digit of 5 or more rounds the preceding digit up in magnitude. This matches how most hand calculations and spreadsheets behave. Some scientific contexts use round-half-to-even instead, which differs only on exact halves.
Why show the result in scientific notation?
Scientific notation makes the number of significant figures unambiguous. Writing 3,100 could mean two, three or four significant figures, but writing 3.1 times 10 to the third clearly shows two. The calculator therefore reports both the ordinary rounded value and the scientific-notation form.
How many significant figures can I request?
You can request any whole number of significant figures from one upward. Requesting more figures than the input actually contains simply pads with the digits already present. This calculator treats a request below one significant figure, or a zero input, as needing care: zero has no significant figures to round and is reported as zero.
Official sources
- National Institute of Standards and Technology: Guidelines for Evaluating and Expressing Uncertainty.
- National Institute of Standards and Technology: SI usage checklist and significant digits.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.