How Many Significant Figures? Examples & Answers
Wondering how many significant figures are in a number? This guide answers that question for 50+ examples. Learn to count sig figs in decimals, whole numbers, and scientific notation.
Visual Example: Counting Sig Figs in 0.00450
Answer: 3 significant figures
Quick Rules: How to Count Significant Figures
Always Significant
- All non-zero digits (1-9)
- Zeros between non-zero digits
- Trailing zeros after decimal point
Never Significant
- Leading zeros (0.00...)
- Trailing zeros without decimal (ambiguous)
How Many Significant Figures: Basic Examples
Let's start with simple numbers. For each example, we'll show how many sig figs and why.
| Number | How Many Sig Figs? | Explanation |
|---|---|---|
| 123 | 3 | All non-zero digits are significant |
| 45.67 | 4 | All non-zero digits count |
| 7 | 1 | Single non-zero digit |
| 3.0 | 2 | Trailing zero after decimal IS significant |
| 100 | 1 | Trailing zeros without decimal are NOT significant |
| 100. | 3 | Decimal point makes all digits significant |
How Many Sig Figs with Zeros Between Digits?
Zeros sandwiched between non-zero digits are always significant. Here's how many significant figures these numbers have:
| Number | How Many Sig Figs? | Explanation |
|---|---|---|
| 101 | 3 | Zero between 1s is significant |
| 5.007 | 4 | All zeros between non-zero digits count |
| 1002.5 | 5 | Both zeros are sandwiched, so significant |
How Many Significant Figures with Leading Zeros?
Leading zeros (zeros before the first non-zero digit) are never significant. They just show decimal placement.
| Number | How Many Sig Figs? | Explanation |
|---|---|---|
| 0.005 | 1 | Leading zeros don't count, only the 5 |
| 0.0420 | 3 | 4, 2, and trailing 0 are significant |
| 0.00001 | 1 | Only the 1 is significant |
How Many Sig Figs with Trailing Zeros?
Trailing zeros are tricky. After a decimal point, they're significant. Without a decimal, they're ambiguous.
Trailing Zeros After Decimal (Significant)
| 2.50 | 3 SF |
| 100.0 | 4 SF |
| 6.000 | 4 SF |
Trailing Zeros Without Decimal (Ambiguous)
| 100 | 1? |
| 1000 | 1? |
| 500 | 1? |
How to remove ambiguity: 1.00×10², 1.0×10², 1×10²
How Many Significant Figures in Scientific Notation?
Scientific notation makes counting sig figs easy. All digits in the coefficient are significant.
| Number | How Many Sig Figs? | Explanation |
|---|---|---|
| 3.00×10² | 3 | All coefficient digits count |
| 6.02×10²³ | 3 | Avogadro's number: 3 sig figs shown |
| 1.0×10⁻³ | 2 | 1 and trailing 0 both count |