🔢 Sig Fig Calculator
Count the significant figures in a number, see exactly which digits count and why, and round it to the number of sig figs you need.
Quick answer: 0.004050 has 4 significant figures – the leading zeros don’t count but the trailing zero after the 5 does – and rounded to 2 significant figures it becomes 0.0041.
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Sig Fig Calculator inputs
Result
Significant figures in 0.004050
4
4 significant figures
0.004050
Underlined bold digits are significant; faded zeros are placeholders.
- Scientific notation
- 4.050 × 10⁻³
- Decimal places
- 6
- Rounded to 2 s.f.
- 0.0041
- In scientific notation
- 4.1 × 10⁻³
Step by step
- 2 non-zero digits – always significant
- 1 zero between non-zero digits – significant
- 1 trailing zero after the decimal point – significant
- 3 leading zeros – never significant (they only place the decimal point)
- Total: 4 significant figures
- To round to 2: keep the first 2 significant digits, look at the next digit (5) – 5 or more, so round up
- Result: 0.0041
Rounded to 1–6 significant figures
| Sig figs | Standard form | Scientific notation |
|---|---|---|
| 1 | 0.004 | 4 × 10⁻³ |
| 2 | 0.0041 | 4.1 × 10⁻³ |
| 3 | 0.00405 | 4.05 × 10⁻³ |
| 4 | 0.004050 | 4.050 × 10⁻³ |
| 5 | 0.0040500 | 4.0500 × 10⁻³ |
| 6 | 0.00405000 | 4.05000 × 10⁻³ |
Rules for counting significant figures
- Non-zero digits are always significant: 123 has 3.
- Zeros between non-zero digits (captive zeros) are significant: 1005 has 4.
- Leading zeros are never significant: 0.0025 has 2.
- Trailing zeros after a decimal point are significant: 2.500 has 4.
- Trailing zeros in a whole number with no decimal point are ambiguous: 1500 has 2, 3 or 4. Use scientific notation to be clear.
Count from the first non-zero digit to the last significant digit
Worked example
How many significant figures are in 0.004050?
- The three zeros in 0.00 are leading zeros – not significant.
- 4 and 5 are non-zero – significant.
- The 0 between 4 and 5 is captive – significant.
- The final 0 comes after the decimal point – significant.
That makes 4 significant figures. Rounded to 2: keep 4 and 0, the next digit is 5, so round up to 0.0041.
Examples
| Number | Sig figs | Why |
|---|---|---|
| 3.14159 | 6 | All non-zero |
| 100.0 | 4 | Decimal point makes the zeros count |
| 0.020 | 2 | Leading zeros don’t count, trailing one does |
| 5,000 | 1 (ambiguous) | No decimal point |
| 6.02 × 10²³ | 3 | Only the mantissa counts |
How to use the calculator
Type the number exactly as it was recorded – keep any trailing zeros and the decimal point – and optionally enter how many significant figures to round to. The result highlights each digit so you can see which ones count.
Why significant figures matter
Significant figures communicate how precise a measurement is. Writing 2.50 g instead of 2.5 g says the balance was accurate to a hundredth of a gram. Calculated results should never look more precise than the measurements they came from, which is why lab reports round answers to the correct number of sig figs.
Frequently asked questions
Are trailing zeros significant?
Trailing zeros are significant when the number has a decimal point: 2.50 has 3 significant figures and 1200. has 4. In a whole number without a decimal point, such as 1200, they are ambiguous – usually counted as not significant (2 s.f.). Write 1.20 × 10³ to show exactly 3.
Are leading zeros significant?
No. Zeros before the first non-zero digit, as in 0.0045, only show where the decimal point is. 0.0045 has 2 significant figures.
How do I round to significant figures?
Start counting at the first non-zero digit, keep the required number of digits, and look at the next digit: 5 or more rounds up, less than 5 leaves it. Replace dropped digits to the left of the decimal point with zeros. 48,632 to 2 s.f. is 49,000.
How do sig figs work in calculations?
When multiplying or dividing, round the answer to the fewest significant figures of any input. When adding or subtracting, round to the fewest decimal places instead. Round only at the end to avoid accumulating errors.