string length?

Hi, I am quite new to PHP scripts and I have run into a little problem with my string! I have a string called $numbers which is 5;6;12;21;36;42 (for example, it can be any 6 numbers between 1 and 42). Is there an easy way that I can find out how many numbers there are in the string without the five semi-colons?? I was playing around with count_chars but had no success! then i tried converting it to an array and counting the number of elements in the array but unfortunatley it put the whole string in as the first element of the array and returned a size of 1! I would appreciate any help you can give me, Cheers, Kevin.