Significant Figures Calculator

Count significant digits and round a number to the precision your measurement supports.

Type it exactly as written, including trailing zeros. 4.050e-3 also works.

How to use the Significant Figures Calculator

  1. Enter the number – Type it exactly as written, including trailing zeros. 4.050e-3 also works.
  2. Enter the round to how many sig figs (optional).
  3. Press Calculate. The result updates automatically as you type.

About the Significant Figures Calculator

Significant figures show how precisely a number was measured. A scale that reads 0.004050 g is claiming accuracy to the millionth of a gram, and the final zero matters: it says the digit was measured and found to be 0. Chemistry, physics and engineering courses expect results to carry no more significant figures than the least precise measurement that went into them.

For multiplication and division, round the answer to the fewest sig figs of any input; for addition and subtraction, round to the fewest decimal places. Type numbers as text exactly as written, because 12.0 and 12 are different measurements even though they are the same value. The bold digits in the result are the ones that count.

Formula

Rules for counting significant figures:

  1. All non-zero digits are significant.
  2. Zeros between non-zero digits are significant (1,005 has 4).
  3. Leading zeros are never significant (0.0045 has 2).
  4. Trailing zeros are significant only if there is a decimal point (12.00 has 4; 1200 has 2, ambiguous).

To round to n sig figs, keep the first n significant digits and round on the next one.

Example calculation

Using the default values:

  • Number = 0.004050
  • Round to how many sig figs (optional) = 2

the calculator returns:

  • Significant figures: 4
  • Significant digits (bold): 0.004050
  • Rounded value: 0.0041
  • Rounded, scientific notation: 4.1 × 10^-3

Frequently asked questions

How many significant figures are in 0.004050?

Four: 4, 0, 5 and the final 0. The leading zeros only locate the decimal point.

How many sig figs does 1200 have?

It is ambiguous; by convention two. Writing 1200. or 1.200 × 10³ shows four.

Do exact numbers limit significant figures?

No. Counted quantities (12 eggs) and defined constants (100 cm in 1 m) are exact and have unlimited significant figures.

Last updated: · Category: Math calculators

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