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Significant Figures Calculator

Count sig figs in a number, or round to however many you need

Enter a number to count its significant figures, or round it to a chosen number of sig figs.

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Significant figures in this number
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Rounded to the chosen number of sig figs
Rules used: all non-zero digits count; zeros between non-zero digits count; leading zeros never count; trailing zeros only count if there's a decimal point. Scientific notation (e.g. 4.05e-3) counts only the digits in the coefficient.

What significant figures are

Significant figures (sig figs) are the digits in a number that carry meaningful information about its precision. A measurement written as 12.30 cm says you measured to the hundredth of a centimetre; 12.3 cm says you only measured to the tenth. In science, engineering and lab work, quoting a result with more sig figs than your measurements support implies a precision you don't have.

The counting rules

  1. All non-zero digits count: 482 has 3.
  2. Zeros between non-zero digits count: 4,005 has 4.
  3. Leading zeros never count: 0.0072 has 2.
  4. Trailing zeros count only if there's a decimal point: 45.00 has 4; 4,500 is ambiguous (taken as 2).
  5. In scientific notation, only the coefficient counts: 4.50 × 103 has 3.

Worked examples

  • 0.004050 → leading zeros don't count; 4, 0, 5 and the trailing 0 after the decimal do → 4 sig figs
  • 3.14159 rounded to 3 sig figs → 3.14
  • 86,472 rounded to 2 sig figs → 86,000 (written 8.6 × 104 to make the precision clear)

FAQ

How many sig figs should my answer have when multiplying or dividing?

As many as the input with the fewest sig figs. 4.56 × 1.4 = 6.384, which rounds to 6.4 (2 sig figs, because 1.4 has 2).

What about adding and subtracting?

There the rule is decimal places, not sig figs: round to the fewest decimal places among the inputs. 12.11 + 0.3 = 12.41, which rounds to 12.4.

How do I show that the zeros in 1,500 are significant?

Use scientific notation (1.500 × 103 for 4 sig figs) or add a decimal point (1500.). Otherwise trailing zeros in a whole number are ambiguous.

Do exact numbers limit sig figs?

No. Counted items (12 eggs) and defined values (100 cm in a metre) are exact and treated as having unlimited sig figs.

Related tools

Rounding Scientific Notation Percent Error Statistics Scientific Calculator Chemistry