Sig Fig Calculator – Count and Round Significant Figures
Find out how many significant figures a number has and round it to any number of sig figs, with the rules for leading, trailing and captive zeros explained.
Non-zero digits are always significant, zeros between them are significant, leading zeros never are, and trailing zeros count only if there is a decimal point. So 0.004560 has 4 significant figures (4, 5, 6 and the final 0), and rounded to 2 sig figs it is 0.0046.
How to use Significant Figures Calculator
- Type the number exactly as written, including trailing zeros.
- Read the number of significant figures.
- Enter how many sig figs you want to round to.
- Read the rounded value and its scientific notation.
- Use the rules below to check your homework.
Why significant figures matter
Significant figures (sig figs) show how precise a measurement is. Writing 2.50 m says the length was measured to the nearest centimetre; writing 2.5 m says only to the nearest ten centimetres. In science and engineering, a result should not claim more precision than the data it came from.
The rules
- Non-zero digits are always significant. 123 has 3.
- Zeros between non-zero digits are significant. 1,005 has 4.
- Leading zeros are never significant. 0.0045 has 2.
- Trailing zeros are significant only with a decimal point. 2.500 has 4; 2,500 is ambiguous.
- In scientific notation, every digit of the coefficient counts. 2.50 × 10³ has 3.
Examples
| Number | Sig figs | Why |
|---|---|---|
| 4,507 | 4 | Zero between digits counts |
| 0.00380 | 3 | Leading zeros don’t count; trailing zero after the point does |
| 120.0 | 4 | Decimal point makes all zeros count |
| 1,200 | 2 (ambiguous) | Write 1.20 × 10³ for 3 |
| 6.020 × 10²³ | 4 | All coefficient digits count |
Numbers like 1,200 are ambiguous: they could have 2, 3 or 4 significant figures. The calculator counts them as 2 and tells you so. To make the precision clear, use scientific notation — the Scientific Notation Converter converter helps.
Rounding to significant figures
Count from the first non-zero digit, keep the number of digits you need and round the next digit: 0.004560 to 2 sig figs is 0.0046; 98,765 to 3 sig figs is 98,800 (better written 9.88 × 10⁴).
Calculations with sig figs
- Multiplying and dividing: the result has as many sig figs as the least precise input. 2.5 × 3.42 = 8.55 → 8.6.
- Adding and subtracting: the result keeps as many decimal places as the input with the fewest. 12.11 + 0.3 = 12.41 → 12.4.
Round only at the end of a calculation to avoid rounding errors. For averages and spread of measurements, see the Standard Deviation Calculator calculator.
You may also find these free tools useful: GPA Calculator, LCM & GCF Calculator and Slope Calculator.
Frequently asked questions
How many significant figures does 0.004560 have?
Four: 4, 5, 6 and the trailing zero. The leading zeros are not significant.
Are trailing zeros significant?
Only if the number has a decimal point. 2.500 has four sig figs; 2,500 without a decimal point is ambiguous.
How do you round to 3 significant figures?
Start at the first non-zero digit, keep three digits and round using the fourth: 0.045678 becomes 0.0457.
Are zeros between digits significant?
Yes. Zeros between non-zero digits always count, so 1,005 has four significant figures.
How many sig figs in a multiplication result?
As many as the input with the fewest significant figures.
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