Quick answer
Significant figures count the meaningful digits: leading zeros never count, and trailing zeros count only after a decimal point. 0.004500 has 4 significant figures (4, 5, 0, 0).
Enter a number. The calculator returns the number of significant figures.
Related tools: Significant Figures Calculator: Count significant figures and round to a chosen number. Fraction Calculator: Add, subtract, multiply and divide fractions with simplified and mixed-number results. Ratio Calculator: Simplify a ratio of two whole numbers.
How to use the Sig Fig Calculator
- Type number, for example 0.004500.
- Optionally, enter round to (sig. figs) (a whole number, between 1 and 15).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Number | Text, such as 0.004500 | — |
| Round to (sig. figs) (optional) | A whole number | ≥ 1, ≤ 15 |
Formula and method
Formula
Leading zeros never count; trailing zeros count only after a decimal point
IEEE-754 double precision; shown to at most 6 decimal places.
Counts significant digits from the written form, so 1200 has 2 and 1200. has 4; rounds with toPrecision.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Number = 0.004500.
| Result | Value |
|---|---|
| Significant figures | 4 |
Example 2
Inputs: Number = 1200.
| Result | Value |
|---|---|
| Significant figures | 2 |
Example 3
Inputs: Number = 3.14159; Round to (sig. figs) = 3.
| Result | Value |
|---|---|
| Significant figures | 6 |
| Rounded | 3.14 |
The first line is the headline result (significant figures). IEEE-754 double precision; shown to at most 6 decimal places.
The rules
Non-zero digits always count. Zeros between non-zero digits count (1,002 has 4). Leading zeros do not (0.0045 has 2). Trailing zeros count only with a decimal point: 4.500 has 4, but 4500 is ambiguous.
Ambiguity
A number like 1,200 could have 2, 3 or 4 significant figures; this calculator treats trailing zeros without a decimal point as not significant, so it reports 2. Scientific notation removes the ambiguity: 1.20 × 10³ has 3.
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Number: entering "abc" shows "Enter a number such as 0.004500 or 1.20e3." beside that field and no result.
Choosing between the Sig Fig Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Significant Figures Calculator](/math/significant-figures-calculator/) | number | Significant figures |
| [Fraction Calculator](/math/fraction-calculator/) | numerator 1, denominator 1 and operation | Result |
| [Ratio Calculator](/math/ratio-calculator/) | first number and second number | Simplified ratio |
| [Average Calculator](/math/average-calculator/) | numbers | Average (mean) |
| [Long Division Calculator](/math/long-division-calculator/) | dividend and divisor | Quotient |
Background: rounding and basic arithmetic
Rounding to a place looks at the digit just to its right: 0 to 4 rounds down and 5 to 9 rounds up (the half-up convention, so 2.5 becomes 3). Rounding 838.274 gives 800 to the nearest hundred, 840 to the nearest ten and 838 to the nearest one.
Some systems use banker's rounding (half to even), which sends 2.5 to 2 and 3.5 to 4; check which convention your task requires, and round only at the end of a multi-step calculation.
Assumptions and limitations
- Trailing zeros without a decimal point are ambiguous and treated as not significant
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for number to confirm this.
Frequently asked questions
How many sig figs in 100.0?
100.0 has four significant figures, because the trailing zeros after a decimal point count.
How many in 0.0820?
0.0820 has three significant figures (8, 2 and the final 0); the leading zeros don't count.
Why do sig figs matter?
They show the precision of a measurement.
What does the Sig Fig Calculator calculate?
Quick sig fig counter: enter a number to see how many significant figures it has, with optional rounding. It returns Significant figures.
What formula does the Sig Fig Calculator use?
Leading zeros never count; trailing zeros count only after a decimal point. Counts significant digits from the written form, so 1200 has 2 and 1200.
What do I need to enter in the sig Fig Calculator?
You enter Number. Optional: Round to (sig. figs).
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. Trailing zeros without a decimal point are ambiguous and treated as not significant.
What is an example of a sig Fig result?
With number 0.004500, the significant figures is 4.
Where does the method come from?
The method follows: Standard significant-figure rules (e.g. NIST Guide to the SI, §7).
Related calculators
- Significant Figures Calculator — Count significant figures and round to a chosen number.
- Fraction Calculator — Add, subtract, multiply and divide fractions with simplified and mixed-number results.
- Ratio Calculator — Simplify a ratio of two whole numbers.
- Average Calculator — Arithmetic mean, sum, count, minimum and maximum of a list of numbers.
- Long Division Calculator — Divide whole numbers to a chosen number of decimal places.
- Percent Off Calculator — Find the sale price and savings after a percentage discount.
Sources
- Standard significant-figure rules (e.g. NIST Guide to the SI, §7)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.