Significant Figures Calculator

Count the significant figures in a number and round it to any number of sig figs.

Type it exactly as written — trailing zeros and decimal points matter.

Significant figures
4
Digits in the number
Significant: 4 (57.1%)Leading zeros: 3 (42.9%)4sig figs
  • Significant457.1%
  • Leading zeros342.9%
Rounded
0.0046
Rounded (scientific notation)
4.6 × 10⁻³
Significant digits
4560
Show the working
  1. Leading zeros (3) are never significant — they only place the decimal point
  2. Trailing zeros after a decimal point are significant
  3. Significant digits: 4 5 6 0 → 4 sig figs
  4. Rounding to 2: look at digit 3 of 4560 (6) — round up
  5. Result: 0.0046 = 4.6 × 10⁻³

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Formula

1. Non-zero digits are always significant2. Zeros between non-zero digits are significant3. Leading zeros are never significant4. Trailing zeros count only if the number has a decimal point

How it works

Significant figures (sig figs) are the digits in a measurement that carry real information about its precision. Writing 2.50 cm instead of 2.5 cm says you measured to the nearest hundredth of a centimetre, so the trailing zero counts.

The tricky part is zeros. Leading zeros, as in 0.0045, only show where the decimal point is, so they are not significant — 0.0045 has two sig figs. Zeros sandwiched between other digits, like the 0 in 305, always count. Trailing zeros count when there is a decimal point (4.500 has four), but in a whole number like 1200 they are ambiguous, and most courses treat them as not significant.

To round to a given number of sig figs, keep that many digits starting from the first non-zero digit, and look at the next digit: 5 or more rounds up, less than 5 leaves it alone. Replace dropped digits to the left of the decimal point with zeros so the size of the number doesn’t change.

Frequently asked questions

How many sig figs does 100 have?

By the usual convention, one. Writing “100.” with a decimal point means three, and 1.0 × 10² means two. Scientific notation removes the ambiguity.

How do sig figs work in multiplication and division?

Round the answer to the smallest number of significant figures among the values you multiplied or divided. 2.5 × 3.14159 = 7.9 (two sig figs).

And in addition and subtraction?

There the rule is about decimal places, not sig figs: round to the fewest decimal places among the numbers. 12.11 + 0.3 = 12.4.

Do exact numbers limit sig figs?

No. Counted quantities (12 eggs) and defined constants (100 cm in a metre) are exact and have unlimited significant figures.

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