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Significant Figures Calculator (Sig Fig Counter & Rounder)

This significant figures calculator counts sig figs in a number you type, rounds to N significant figures, and applies sig-fig rules to addition, subtraction, multiplication, and division.

What do you want to do?

Type numbers as text so leading and trailing zeros stay put. Scientific notation such as 1.20e3 or 1.20 × 10^3 is allowed.

Examples: 0.00450, 100, 100., and 1.20 × 10^3.

Result

3 significant figures

0.00450 has 3 significant figures. Leading zeros are not significant, and trailing zeros after a decimal point are significant.

Written as 0.00450. The count stays in your browser.

How to use

  1. Choose Count, Round, or Arithmetic.
  2. Type each number as text. Leading zeros, trailing zeros, and scientific notation such as 1.20e3 or 1.20 × 10^3 are kept.
  3. For rounding, choose how many significant figures to keep. For arithmetic, choose add, subtract, multiply, or divide.
  4. Read the count or the rounded result, then use Clear to empty the inputs.

Formula

Nonzero digits are significant. Zeros between nonzero digits are significant. Leading zeros are not. Trailing zeros are significant only when the number has a decimal point, so 100 has 1 significant figure, 100. has 3, and 0.00450 has 3. In scientific notation, the coefficient carries the significant figures. Rounding looks at the first dropped digit and rounds half up. Multiplication and division keep as many significant figures as the less precise number. Addition and subtraction round to the least precise decimal place.

Example. 0.00450 has 3 significant figures. Rounding 12345 to 3 significant figures gives 1.23 × 10^4. Multiplying 2.5 × 3.42 gives 8.55, which rounds to 8.6. Adding 12.11 + 18.0 gives 30.11, which rounds to the tenths place as 30.1.

Example. 100 has 1 significant figure because it has no decimal point. 100. has 3, and 1.20 × 10^3 has 3.

Example. 6.00 ÷ 2.0 has 2 significant figures in the less precise number, so the quotient is 3.0.

Frequently asked questions

How do you count significant figures?

Count every nonzero digit and every zero between nonzero digits. Leading zeros are placeholders, so 0.00450 has 3 significant figures: 4, 5, and the trailing 0. In scientific notation, count the digits in the coefficient. 1.20 × 10^3 has 3.

Are trailing zeros significant?

Trailing zeros are significant when the number contains a decimal point. 100. has 3 significant figures and 2.0 has 2. A whole number with no decimal point, such as 100 or 4500, does not treat those trailing zeros as significant, so 100 has 1 and 4500 has 2.

How do you round to N significant figures?

Keep the first N significant digits and look at the next digit. If it is 5 or more, round the kept digits up; otherwise leave them. 12345 to 3 significant figures is 1.23 × 10^4. 1.235 to 3 significant figures is 1.24. 999 to 2 significant figures is 1.0 × 10^3.

What sig fig rule applies to multiplication and division?

The result has as many significant figures as the number with the fewest. 2.5 × 3.42 = 8.55, and 2.5 has 2 significant figures, so the result is 8.6. 6.00 ÷ 2.0 keeps 2 significant figures, so the quotient is 3.0.

What sig fig rule applies to addition and subtraction?

Round the result to the least precise decimal place, not to the smaller count of significant figures. 12.11 is precise to the hundredths and 18.0 is precise to the tenths, so 12.11 + 18.0 = 30.11 rounds to 30.1. A whole number such as 100, with no decimal point, is precise only to the hundreds place.

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