plainlySigFig calculator
Every meaningful digit, counted.
Find significant figures and round with care.
Rounded number
0.00123
Scientific notation: 1.23e-3
- Input significant figures
- 4
- Rounded to
- 3 significant figures
Leading zeros set the scale; zeros after the first nonzero digit count when decimal or scientific notation makes the precision explicit.
Updates as you type. Exact decimal digit rounding. Your input stays in this tab.
Which digits
count?
A sigfig calculator counts significant figures—the digits used to express a measurement’s precision. Enter the number as written, including its decimal point and trailing zeros. The tool can count those digits and round the value to a chosen number of significant figures.
Zeros have different jobs
Nonzero digits count, as do zeros between them. Leading zeros only locate the decimal point. Trailing zeros in decimal notation indicate precision. Whole-number trailing zeros can be ambiguous, so this tool assumes they are placeholders unless a decimal point or scientific notation makes them explicit.
| As written | Count | Why |
|---|---|---|
| 0.001230 | 4 | The final zero counts. |
| 1002 | 4 | Both interior zeros count. |
| 1200 | 2 assumed | Trailing zeros are ambiguous. |
| 1200. | 4 | The decimal point states precision. |
| 1.20e3 | 3 | Only coefficient digits count. |
These counting conventions and the default half-to-even rule follow the OpenStax explanation of measurement precision. Numbers alone cannot reveal an instrument’s accuracy.
Round once.
State the precision.
Significant figures versus decimal places
Significant figures start at the first nonzero digit. Decimal places count positions after the decimal point. For example, 0.00456 has three significant figures and five decimal places. Rounding it to two significant figures gives 0.0046.
What happens at an exact tie?
With half to even, 2.45 rounded to two significant figures becomes 2.4 because the retained digit is even; 2.55 becomes 2.6. With half away from zero, 2.45 becomes 2.5 and −2.45 becomes −2.5. If any nonzero digit follows the discarded 5, the value is past the tie: 2.4501 rounds to 2.5 under either rule.
Why show scientific notation?
A rounded whole number can hide how many digits you intended. For example, 1234 rounded to three significant figures is written as 1230, but 1.23e3 makes the three-digit precision clear. The e3 means “times 10 to the power of 3.”
Limits and exact digits
The converter uses the written decimal digits, including a carry across powers of ten, instead of first turning the value into a binary floating-point number. Inputs allow up to 100 coefficient digits and exponents from −1000 to 1000. Choose 1–15 output significant figures. This is a counting and rounding tool, not an arithmetic expression calculator.
Good questions.
Straight answers.
How many significant figures are in 0.001230?
Four: 1, 2, 3, and the final zero. The leading zeros set the scale and do not count. Rounded to three significant figures, it is 0.00123.
How many significant figures are in 1000?
The notation is ambiguous. This tool assumes one when there is no decimal point. Use 1.00e3 for three significant figures, or 1.000e3 for four.
Can I round negative numbers?
Yes. The magnitude is rounded using the chosen rule, then the minus sign is retained. The sign does not count as a significant figure.
What happens if rounding carries into a new digit?
For example, 9.99 rounded to two significant figures becomes 10, shown explicitly as 1.0e1. The scientific form preserves the two-digit precision.
How does the tool handle zero?
Zero has no first nonzero digit. The tool returns 0 and leaves its significant-figure count undetermined. Use decimal places or a stated uncertainty to express the precision of a zero measurement.
Does adding zeros make a measurement more accurate?
No. Choosing more digits can format a value with extra trailing zeros, but it cannot supply information the measurement never had.
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