Significant Figures Calculator
Count sig figs with digit-by-digit highlighting, round to any precision, or do arithmetic with proper sig fig rules.
New to significant figures? Read the Numbers, Units & Measurement study guide →
How It Works
Significant figures indicate the precision of a measurement. The rules are straightforward: all non-zero digits are significant, zeros between non-zero digits (captive zeros) are significant, and trailing zeros after a decimal point are significant. Leading zeros are never significant.
When performing arithmetic, the result must reflect the precision of the least precise input. For addition and subtraction, round to the least precise place value. For multiplication and division, round to the fewest significant figures.
Trailing zeros without a decimal point are not significant, so 100 has 1 sig fig. Writing 100. (with a trailing decimal) makes it 3 sig figs. Scientific notation (1.00 × 10²) is the clearest way to show precision.
Reference: OpenStax Chemistry 2e, Measurement Uncertainty, Accuracy, and Precision.
Frequently Asked Questions
What are significant figures?
Significant figures are the digits in a measurement that carry meaningful precision: all the certain digits plus the first uncertain one. They communicate how precisely a quantity was measured.
What are the rules for counting significant figures?
All non-zero digits are significant. Zeros between non-zero digits are significant. Trailing zeros after a decimal point are significant. In a whole number without a decimal point, trailing zeros are not significant. Leading zeros are never significant.
How many significant figures does 100 have?
Written as 100, it has 1 significant figure because its trailing zeros are not significant. Writing 100. with a trailing decimal point makes it 3, and 1.00 × 10² is another clear way to show 3 significant figures.
How do significant figures work in calculations?
For multiplication and division, the result keeps the fewest significant figures of any input. For addition and subtraction, the result is rounded to the least precise decimal place.
Are leading zeros significant?
No. Leading zeros only fix the position of the decimal point. In 0.00450 the leading zeros are not significant, so the number has 3 significant figures.