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Significant Figures Calculator

Count the significant figures in a number, and round any number to the significant figures you choose, with the rules explained.

Results

ItemValue

Steps

StepWorking
For whole numbers with trailing zeros and no decimal point, such as 1500, the zeros are ambiguous. This calculator does not count them, which is the most common convention. Write 1500. or 1.500 × 10³ to show they are significant.

Quick Answer

Significant figures are the digits in a number that carry meaning. Non-zero digits always count, zeros between them count, leading zeros never count, and trailing zeros count only after a decimal point. So 0.004560 has 4 significant figures (4, 5, 6 and the final 0). Rounded to 2, it is 0.0046.

Last updated: 2 November 2026 ·How we calculate this: standard significant figure rules

Table of Contents

How This Significant Figures Calculator Works

Type a number exactly as it is written, including any trailing zeros and decimal point. The calculator applies the significant figure rules and shows how each kind of zero is treated. Enter a number of significant figures to round to, and it gives the rounded answer in standard and scientific form.

Quick explanation: count from the first non-zero digit. Count trailing zeros only if there is a decimal point.

  • Type it as written: 2.50 and 2.5 have different counts.
  • Scientific notation: you can type 1.20e3.
  • Rounding: optional, from 1 to 15 significant figures.

How to Use the Significant Figures Calculator

  1. Type your number exactly as written, including zeros and any decimal point.
  2. Optionally, enter how many significant figures to round to.
  3. Press Calculate.
  4. Read the count, the decimal places and the rounded answers.
  5. Check the steps to see which zeros counted and why.

The Significant Figure Rules

  1. Non-zero digits are always significant: 123 has 3.
  2. Zeros between non-zero digits are significant: 1,005 has 4.
  3. Leading zeros are never significant: 0.0025 has 2.
  4. Trailing zeros after a decimal point are significant: 2.500 has 4.
  5. Trailing zeros in a whole number with no decimal point are ambiguous: 1,500 has 2, 3 or 4.

Key Terms

  • Significant figures: the digits in a number that show its precision.
  • Leading zeros: zeros before the first non-zero digit, such as in 0.005.
  • Trailing zeros: zeros at the end of a number, such as in 2.500.
  • Precision: how finely a measurement is recorded.
  • Exact number: a value with no uncertainty, such as a count of objects.

Worked Example

Round 0.004560 to 2 significant figures.

  • Leading zeros (0.00) do not count
  • The significant digits are 4, 5, 6 and 0, so it has 4 significant figures
  • Keep the first two: 4 and 5. The next digit is 6, so round up to 46
  • Answer: 0.0046, or 4.6 × 10^-3

Real-Life Examples

  • A lab report: a mass of 12.30 g has 4 significant figures, so the scale read to the hundredth of a gram.
  • Multiplying measurements: 2.5 cm × 3.42 cm = 8.55 cm², but 2.5 has only 2 significant figures, so report 8.6 cm².
  • Adding measurements: 12.1 g + 0.235 g = 12.335 g, rounded to one decimal place as 12.3 g.
  • Large numbers: a population of 8,100,000 stated to 2 significant figures is clearer as 8.1 × 10⁶.

Significant Figures vs Decimal Places

  • Significant figures: count meaningful digits from the first non-zero digit. 0.0520 has 3.
  • Decimal places: count digits after the decimal point. 0.0520 has 4.
  • When to use each: sig figs for multiplying and dividing, decimal places for adding and subtracting.

Examples at a Glance

NumberSignificant figuresWhy
4823All non-zero
1,0054Zeros between digits count
0.00252Leading zeros do not count
2.5004Trailing zeros after a decimal count
1,5002Trailing zeros without a decimal are ambiguous
1500.4The decimal point makes the zeros count
3.00 × 10⁴3All digits in the coefficient count

Significant Figures in Calculations

  • Multiplying and dividing: round the answer to the fewest significant figures in the inputs.
  • Adding and subtracting: round to the fewest decimal places in the inputs.
  • Exact numbers: counted items and defined values, such as 12 in a dozen, have unlimited significant figures.
  • Round at the end: keep extra digits during working to avoid rounding errors.

Common Mistakes to Avoid

  • Counting leading zeros. 0.007 has only 1 significant figure.
  • Dropping meaningful zeros. 2.50 and 2.5 are different measurements.
  • Using sig figs for addition. Use decimal places when adding or subtracting.
  • Rounding at every step. Round once, at the end.
  • Applying limits to exact numbers. Counts and definitions are exact.

Frequently Asked Questions

4: the digits 4, 5, 6 and the final 0.

Yes after a decimal point, as in 2.50. In whole numbers without a decimal point, such as 1500, they are ambiguous.

Usually 1, unless written as 100. or 1.00 × 10², which show 3.

Find the first non-zero digit, count across to the number you need, and round using the next digit.

Just 0 is often treated as 1. 0.00 shows precision to two decimal places.

They show how precise a measurement is, so answers do not claim more accuracy than the data supports.

Count every digit in the coefficient. 6.020 × 10²³ has 4.

3.14. The fourth digit is 1, so the third digit stays the same.

The first non-zero digit is 4. Keep 4 and 8, and the next digit is 5, so round up to 0.00049.

Round the answer to the smallest number of significant figures among the numbers you multiplied.

References & Sources

SourceUsed ForLink
Wikipedia, Significant figures Rules for significant figures. https://en.wikipedia.org/wiki/Significant_figures
NIST, Guide for the use of the SI Rounding and expressing values. https://www.nist.gov/pml/special-publication-811