Sig Figs Calculator
Count significant figures with the rule that applied, and round to any.
About this calculator
Type a number and get its significant-figure count with the specific rule explained โ why 0.004560 has four but 4560 has three โ plus a rounder that rewrites the number to any chosen precision, keeping the trailing zeros that matter.
The rules, and why they exist
Sig figs encode honesty about measurement: writing 4.56 claims you measured to the hundredth, and the rules exist so that claim survives arithmetic. The complete set: non-zero digits always count; zeros between them count (405 has three); leading zeros never count โ they only place the decimal; trailing zeros count only with a decimal point present, which is the rule that does all the damage in class. The ambiguity it leaves (does 4560 claim three figures or four?) is exactly why scientific notation exists: 4.560 ร 10ยณ says four figures unambiguously. In calculations, the convention is that multiplication keeps the fewest sig figs of any input, addition the fewest decimal places โ your final answer can't be more honest than your worst measurement.
Frequently asked questions
How many sig figs does 0.004560 have?
Four: 4, 5, 6, and the trailing zero โ which counts because there's a decimal point. The leading zeros never count; they only position the decimal.
Do trailing zeros count as significant?
With a decimal point, yes (2.400 has four). Without one, they're ambiguous and conventionally not counted (2400 has two) โ write scientific notation to claim them explicitly.
How many sig figs should my answer have?
For multiplication and division, match the input with the fewest sig figs; for addition and subtraction, the fewest decimal places. The answer can't outclaim the least precise measurement.
Why do significant figures matter?
They carry the precision of a measurement through the maths โ 4.56 and 4.5600 are the same number but different claims about how well you measured. Sig figs stop calculators inventing precision.