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Significant Figures Calculator

Count significant figures, round numbers, and apply significant-figure rules to addition, subtraction, multiplication and division.

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About this calculatorThis calculator follows standard significant-figure rules for common arithmetic operations and supports scientific notation.

Enter Calculation

Scientific notation is supported: 1.20e3, 6.02e23, -0.00500. Whole-number trailing zeros can be ambiguous; use notation such as 1e2 (1 s.f.), 1.0e2 (2 s.f.) or 1.00e2 (3 s.f.) to show the intended precision.

What are Significant Figures?

Significant figures are the digits in a number that communicate meaningful measurement precision. They help show how precisely a value is known.

Rules Summary

  • For addition and subtraction, round to the least precise decimal place.
  • For multiplication and division, round to the fewest significant figures.
  • Non-zero digits and interior zeros are significant.
  • Leading zeros are not significant.
  • Trailing decimal zeros are significant; whole-number trailing zeros can be ambiguous without notation.

Examples

12.3 + 4.56 = 16.9  (3 s.f.)
5.2 × 3.1 = 16  (2 s.f.)
100.0 ÷ 3.00 = 33.3  (3 s.f.)
0.00450 × 2.0 = 0.0090  (2 s.f.)

How to Use a Significant Figures Calculator

A significant figures calculator helps you count meaningful digits, round a number to a chosen precision, and apply measurement-precision rules to arithmetic. Enter the value as written, including its decimal point or scientific notation, so its intended precision is clear.

How to round to significant figures

  1. Start at the first non-zero digit. This is the first significant digit.
  2. Count the required number of significant digits from left to right.
  3. Look at the next digit: if it is 5 or greater, increase the last kept digit by one; otherwise leave it unchanged.
  4. Use decimal places or scientific notation to make the final precision unambiguous.

For example, 0.004567 rounded to 3 significant figures is 0.00457. The leading zeros locate the decimal point; they do not count as significant digits.

Significant figures in addition and subtraction

For addition and subtraction, the result is limited by the input with the fewest decimal places. For example, 12.11 + 18.0 = 30.11, which is reported as 30.1 because 18.0 is precise only to the tenths place.

Significant figures in multiplication and division

For multiplication and division, report the result with the same number of significant figures as the input with the fewest significant figures. For example, 2.50 × 4.0 = 10.0 before rounding, so the reported result is 1.0 × 10¹ (2 significant figures), which makes the precision clear.

Zeros and scientific notation

Exact counted quantities and defined conversion factors do not limit significant figures in the same way as measured values. Keep unrounded digits during intermediate steps and round the final answer once.

Frequently Asked Questions

Significant figures indicate the meaningful precision communicated by a measured or calculated number.
Count non-zero digits and interior zeros as significant, exclude leading zeros, and treat trailing decimal zeros as significant. Trailing zeros in whole numbers can be ambiguous without notation.
Report the result with the same number of significant figures as the input with the fewest significant figures.
Find the first non-zero digit, keep three significant digits, and use the next digit to decide whether to round the third digit up. For example, 0.004567 becomes 0.00457.
Keep the first three significant digits. The next digit is 1, so 45.51 rounds to 45.5.
There are 4 significant figures: the leading zeros are placeholders, while 4, 5, 6 and the final decimal zero are significant.
Write it as 1.2 × 10³ (1.2e3). Scientific notation makes the two significant digits clear.
Decimal places count digits to the right of the decimal point. Significant figures count meaningful digits starting with the first non-zero digit. Addition and subtraction use decimal-place precision; multiplication and division use significant-figure precision.