Chem Sig Fig

Non-zero digits rule

All non-zero digits are always significant (e.g., $123.45$ has $5$ significant figures).

Captive zeros rule

Zeros located between two non-zero digits are always significant (e.g., $1005$ has $4$ significant figures).

Leading zeros rule

Zeros at the beginning of a number before any non-zero digits are never significant (e.g., $0.0025$ has $2$ significant figures).

Trailing zeros rule with a decimal point

Zeros at the end of a number are significant if the number contains an explicit decimal point (e.g., $50.0$ has $3$ significant figures).

Trailing zeros rule without a decimal point

Zeros at the end of a number without a decimal point are not significant, serving only as placeholders (e.g., $500$ has $1$ significant figure).

Significant figures rule for addition and subtraction

The calculated result must be rounded to match the fewest number of decimal places present in any of the starting values (e.g., $12.11 + 0.3 = 12.4$).

Significant figures rule for multiplication and division

The calculated result must be rounded to match the fewest total number of significant figures present in any of the starting values (e.g., $2.5 \times 3.42 = 8.6$).

Exact numbers rule

Numbers derived from counting objects or defined unit conversions possess an infinite number of significant figures and do not limit the precision of a calculation (e.g., $12$ inches in $1$ foot).