MATLAB does not distinguish between numbers with trailing zeros after the decimal point. That is, 0.25 == 0.250 == 0.250000000. They are all identically the same numbers. (I won't even get into the question about if 0.3 is really exactly the fraction 3/10, as many people expect. It is not.)
However, if your number is in character representation, as you have written it, then counting the number of digits after the decimal point is easy. Just locate where the decimal point lies. Then locate the last digit in the number. Assuming the string in question is only one number, and there are no trailing spaces, then this will work:
N = '0.25000';
numel(N) - find(N == '.')
You would need to worry about cases with trailing white space, then worry about cases where there was no decimal point, like the number '25', which has zero digits to the right of the decimal point. The trick there, is if a number has no decimal point, then implicitly, there is a decimal point at the very end. So if there is no decimal point found, then add a decimal point as a new last character to the number.
