Non-zero digits count
Every non-zero digit is significant. In 347, all three digits count because each communicates measured precision.
Rules guide
Significant Figures Rules
The core rules are simple once you separate placeholders from measured precision.
Use the calculatorLeading zeros do not count
Zeros before the first non-zero digit only locate the decimal point. In 0.00450, the zeros before 4 are not significant.
Captive zeros count
Zeros between non-zero digits are significant. In 1002, the two zeros are counted because they sit between measured digits.
Trailing zeros depend on notation
Trailing zeros after a decimal point count. Whole-number trailing zeros without a decimal point are ambiguous, so 100 may mean 1, 2, or 3 significant figures.
Arithmetic uses operation-specific rules
Addition and subtraction follow decimal-place precision. Multiplication and division follow the fewest significant figures.