Significant Figures Calculator
Count significant figures in any number instantly and round to any number of sig figs. Shows all 5 sig fig rules with examples.
Count Significant Figures
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Sig Fig Rules
Use scientific notation to eliminate ambiguity: 1.5 x 10^3 clearly has 2 sig figs, while 1.500 x 10^3 has 4 sig figs.
Significant Figures in Operations
| Operation | Rule | Example | Answer |
|---|---|---|---|
| Multiplication | Fewest sig figs in inputs | 4.56 × 1.4 | 6.4 (2 sig figs) |
| Division | Fewest sig figs in inputs | 9.89 ÷ 2.1 | 4.7 (2 sig figs) |
| Addition | Fewest decimal places | 12.52 + 349.0 | 361.5 (1 decimal) |
| Subtraction | Fewest decimal places | 45.67 - 2.3 | 43.4 (1 decimal) |
| Mixed | Apply rule to each step | (2.1 + 3.45) × 1.2 | 6.7 (2 sig figs) |
Why Significant Figures Matter
Significant figures are not just a classroom convention - they communicate the precision of a measurement. When a scientist reports a result as 12.3 grams, the three significant figures tell other scientists that the measurement was made with a precision of about plus or minus 0.1 grams. Reporting it as 12.30 grams (4 sig figs) implies precision to 0.01 grams.
The rules for significant figures ensure that calculated results don't appear more precise than the original measurements allow. This concept is called precision propagation. If you measure a box as 1.2 meters and 3.456 meters and multiply to get the area, reporting 4.1472 square meters implies you measured to 0.0001 square meter precision - but your first measurement was only good to 0.1 meters.
Common Mistakes to Avoid
The most common mistake is confusing significant figures with decimal places. Decimal places count digits after the decimal point. Significant figures count all meaningful digits starting from the first non-zero digit. The number 0.0045 has 0 digits before the decimal but 2 significant figures (4 and 5).