Significant Figures Calculator
Round a number to a chosen number of significant figures and count how many it already has.
How it works
round to n significant figures: keep n digits starting from the first non-zero one
Significant figures are the digits in a number that carry real precision, counted from the first non-zero digit. Rounding to a chosen number of them keeps that many meaningful digits and drops the rest, nudging the last kept digit up or down. This calculator both counts the significant figures already in your number and rounds it to the target you set.
Worked example
3.14159 has six significant figures. Rounded to 3 significant figures it becomes 3.14 — the next digit is a 1, so the third figure rounds down.
Frequently asked questions
Which digits count as significant?
All non-zero digits count, and zeros between them count. Leading zeros never count, and trailing zeros count only when a decimal point is written — so 0.00450 has three significant figures (4, 5 and the final 0).
Why does 1200 show fewer significant figures than 1200.0?
Without a decimal point, trailing zeros are ambiguous and conventionally not counted, so 1200 reads as two significant figures. Writing 1200. or 1.200 × 10³ makes all four significant.
How is this different from rounding to decimal places?
Decimal places count digits after the point; significant figures count from the first non-zero digit anywhere. 0.004560 has four significant figures but six decimal places.
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This calculator is for educational purposes. Double-check important results before acting on them.