All the reported non-zero numbers in measurement are significant. For example, 22.13 has 4 significant figures.
Zeroes sandwiched anywhere between the non-zero digits are significant. For example, 102.4 has 4 significant figures.
Zeroes to the left of a first non-zero digit are not significant. For example, 007 has 1 figure.
The trailing zeroes or the zeroes to the right of the last non-zero digit are significant if the number has a decimal point otherwise they are insignificant. For example, 0.00001020 has 4 significant figures.