Count the significant figures in a number with a short breakdown of the rule applied, and round a number to a chosen number of significant figures.
Significant figures show how precise a measured or reported value is. Leading zeros are never significant, zeros between non-zero digits always are, and trailing zeros are significant only when a decimal point is present in the number. Scientific notation is handled by counting the figures in the coefficient only, since the power of ten sets the size rather than the precision. Rounding uses standard rounding to the requested number of figures and reports the result in a form that keeps those figures visible.
Are trailing zeros significant? Trailing zeros are significant when the number contains a decimal point, so 1.200 has four significant figures. Without a decimal point they are usually treated as placeholders, so 1200 has two significant figures unless a decimal point is written at the end.
Do leading zeros count as significant figures? No. Leading zeros only position the decimal point, so 0.0012 has two significant figures, the 1 and the 2.