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Significant Figures Calculator

Count how many significant figures a number has, and round any value to a chosen number of significant figures — with leading and trailing zeros handled by the proper rules.

Significant figures
4

0.004560 has 4 significant figures.

Rounded to 3 sig figs
3.14

3.14159 rounded to 3 significant figures = 3.14.

Quick answer

Significant figures are the digits that carry real precision in a number. Non-zero digits always count; zeros between them count; leading zeros never count; and trailing zeros count only when a decimal point is present. So 0.004560 has 4 significant figures and 100.0 has 4. This tool counts the sig figs in a number and rounds any value to the number of sig figs you choose.

Formula & method

To count, the tool reads the number as text: it drops any sign and exponent, strips leading zeros, then counts the remaining digits — keeping trailing zeros only if a decimal point is present (since "1200" is ambiguous but "120.0" is not). To round, it uses JavaScript's toPrecision(n), which keeps the first n significant digits and rounds the rest; the result is shown in plain decimal form where reasonable (1234 to 2 sig figs becomes 1200) and in scientific form only for very large or small numbers.

Examples

Example 1: Trailing zero after a decimal
Input
Count sig figs in 0.004560
Result
4
Why
Leading zeros (0.00) are not significant; the digits 4, 5, 6 and the final trailing 0 are, giving 4 significant figures.
Example 2: Trailing zeros, no decimal
Input
Count sig figs in 1234
Result
4
Why
All four non-zero digits are significant, so 1234 has 4 significant figures.
Example 3: Decimal forces trailing zeros to count
Input
Count sig figs in 100.0
Result
4
Why
Because a decimal point is written, the two zeros and the final 0 all count along with the 1 — that is 4 significant figures.
Example 4: Round to 3 sig figs
Input
Round 3.14159 to 3 sig figs
Result
3.14
Why
Keep the first three significant digits 3, 1, 4; the next digit is 1 (< 5), so 4 stays, giving 3.14.
Example 5: Round a small decimal
Input
Round 0.0023456 to 2 sig figs
Result
0.0023
Why
The first two significant digits are 2 and 3; the next digit is 4 (< 5), so the result is 0.0023.
Example 6: Round a whole number down in precision
Input
Round 1234 to 2 sig figs
Result
1200
Why
Keep 1 and 2; the next digit is 3 (< 5), and the place value is filled with zeros, giving 1200.

When to use this tool

  • Reporting a measurement or lab result to the correct number of significant figures.
  • Checking your answer to a chemistry, physics, or engineering homework problem.
  • Rounding a long calculator result to a sensible precision before writing it down.
  • Deciding how many digits to keep when multiplying or dividing measured quantities.

Common mistakes

  • Counting leading zeros as significant — 0.0045 has only 2 significant figures, not 4 or 6.
  • Assuming trailing zeros never count. In 100.0 the trailing zeros ARE significant because a decimal point is written; in plain 100 they are ambiguous and usually treated as not significant.
  • Treating 1200 and 1200. as the same precision. Without a decimal point trailing zeros are ambiguous; writing 1200. or 1.200 × 10³ makes the zeros significant.
  • Rounding digit-by-digit in stages (e.g. 3.146 to 3.15 to 3.2) instead of rounding once from the original number, which can give the wrong answer.

Frequently asked questions

What counts as a significant figure?

Every non-zero digit is significant, as is any zero between non-zero digits. Leading zeros (before the first non-zero digit) are never significant. Trailing zeros are significant only when a decimal point is present.

Why does 0.004560 have 4 significant figures?

The leading 0.00 just sets the decimal place and does not count. The digits 4, 5, 6 are significant, and the final trailing 0 is significant because it comes after the decimal point — so 4 in total.

Are the zeros in 1200 significant?

In plain form, trailing zeros without a decimal point are ambiguous and are usually treated as not significant, so 1200 is taken as 2 significant figures. Writing 1200. or 1.200 × 10³ makes all four significant.

How do I round 1234 to 2 significant figures?

Keep the first two significant digits, 1 and 2. The next digit is 3, which is less than 5, so you round down and fill the remaining places with zeros: 1200.

Does the calculator handle scientific notation?

Yes. You can enter values like 6.022e23 or 1.23e-4. The exponent sets the scale and is ignored when counting significant figures; the result of rounding is shown in scientific form only for very large or very small numbers.

How many significant figures should my answer have?

For multiplication and division, the result should have as many significant figures as the input with the fewest. For addition and subtraction, match the least precise decimal place instead.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

  • ✓ Free to use
  • ✓ No sign-up required
  • ✓ Runs entirely in your browser — nothing is uploaded.
  • ✓ Formula and method shown above
Last updated: How we calculateReport a correctionDisclaimer

Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.

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