Significant Figures Calculator
Rounding to sig figs, and where the convention breaks down.
Work out Significant Figures. Rounding to sig figs, and where the convention breaks down. Says where the rule comes from.
To 3 significant figures
3.14
Input has 6 as written
Leading zeros never count as significant — they only place the decimal point. Trailing zeros after a decimal point always do, because writing them is a claim about precision: 1.50 asserts the hundredths place was measured, while 1.5 does not.
How the Significant Figures Calculator works
Rounding to a given number of significant figures, with a count of how many the input already carries. The page also flags the case the convention genuinely cannot settle: a whole number ending in zeros could be two, three or four significant figures, and nothing in the number itself resolves it.
Also known as: sig fig calculator · round to significant figures · how many sig figs · significant digits calculator
The rules that are settled
Non-zero digits always count. Zeros between them always count. Leading zeros never count — in 0.00123 they only place the decimal point, leaving three significant figures.
Trailing zeros after a decimal point always count, because writing them is a claim: 1.50 asserts the hundredths place was measured, while 1.5 does not.
The rule that is not
A whole number ending in zeros is genuinely ambiguous. 1500 could be two, three or four significant figures depending on how precisely it was measured, and nothing in the number itself resolves it.
Different sources handle this differently — some count all the zeros, some none, some use a bar or a decimal point to disambiguate. This page counts them and flags the ambiguity rather than quietly picking a side.
Scientific notation removes the problem entirely. 1.5 × 10³ says two figures; 1.500 × 10³ says four. That is one of the reasons the notation exists.
Frequently asked questions
What are significant figures?
The digits that carry real information about precision. Leading zeros never count; trailing zeros after a decimal point always do, because writing them is a claim about how precisely something was measured.
How many significant figures does 1500 have?
Genuinely ambiguous — two, three or four, depending on how it was measured. Nothing in the number settles it, which is why scientific notation exists: 1.5 × 10³ says two, and 1.500 × 10³ says four.
Do leading zeros count?
No. In 0.00123 the zeros only place the decimal point; there are three significant figures.
How do sig figs work in a calculation?
For multiplication and division the result carries as many significant figures as the least precise input. For addition, it is decimal places rather than significant figures that govern.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
<iframe src="https://www.thecalclibrary.com/embed/significant-figures-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Significant Figures Calculator"></iframe>The only condition is that the credit line stays visible. It sits inside the frame, so you do not have to do anything to keep it.
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