Sig Fig Calculator
Enter any number to count its significant figures and optionally round to a specific number of sig figs.
Significant Figures — Rules
Rules for counting sig figs
- All non-zero digits are significant: 1234 → 4 sig figs
- Zeros between non-zeros are significant: 1002 → 4 sig figs
- Leading zeros are NOT significant: 0.0045 → 2 sig figs
- Trailing zeros after a decimal ARE significant: 1.200 → 4 sig figs
- Trailing zeros without a decimal are ambiguous: 1200 → 2–4 sig figs
Examples
| Number | Sig Figs | Reason |
|---|---|---|
| 0.00420 | 3 | 4, 2, 0 (trailing after decimal) |
| 1030.0 | 5 | all digits |
| 5.00 × 10⁵ | 3 | 5, 0, 0 |
| 1200 | 2 | trailing zeros without decimal |
Related Calculators
Rules for Counting Significant Figures
All non-zero digits are significant. Zeros between non-zero digits are significant (e.g., 1002 has 4 sig figs). Leading zeros are never significant (0.0042 has 2). Trailing zeros are significant only if there is a decimal point (1200 has 2 sig figs, but 1200. has 4). These rules matter enormously in science: reporting a measurement as 1.20 g communicates that you measured to the nearest 0.01 g — writing 1.2 g implies lower precision.
Sig Figs in Calculations
For multiplication and division, the result has as many significant figures as the measurement with the fewest. For addition and subtraction, the result is rounded to the least number of decimal places (not sig figs) in any measurement.
| Operation | Calculation | Correct answer |
|---|---|---|
| Multiply | 3.2 × 4.56 | 15 (2 sig figs) |
| Divide | 12.00 / 4.0 | 3.0 (2 sig figs) |
| Add | 12.11 + 3.1 | 15.2 (1 decimal place) |
Significant Figures Rules
Significant figures (sig figs) indicate the precision of a measurement. Rules for counting sig figs: all non-zero digits are significant (345 has 3 sig figs). Zeros between non-zero digits are significant (1002 has 4 sig figs). Leading zeros are not significant (0.0045 has 2 sig figs). Trailing zeros after a decimal point are significant (3.40 has 3 sig figs). Trailing zeros in a whole number are ambiguous (1200 could be 2, 3, or 4 sig figs — use scientific notation to clarify: 1.200 × 10³).
Arithmetic rules: for multiplication and division, the result has the same number of sig figs as the measurement with the fewest sig figs. 12.34 × 1.5 = 18.51 → rounds to 19 (2 sig figs from 1.5). For addition and subtraction, the result retains decimal places equal to the measurement with the fewest decimal places. 10.45 + 1.2 = 11.65 → rounds to 11.6 (one decimal place from 1.2). These rules prevent false precision in reported results.
Significant Figures Examples
| Number | Sig Figs | Notes |
|---|---|---|
| 0.0045 | 2 | Leading zeros not significant |
| 1002 | 4 | Interior zeros count |
| 3.40 | 3 | Trailing zero after decimal counts |
| 1200 | 2–4 | Ambiguous — use scientific notation |
| 1.200 × 10³ | 4 | Trailing zeros explicit |
| 100.0 | 4 | Decimal point makes zeros significant |
