Depends on what you mean. There is a different width size ranging from 6" to 9" and a different length ranging from 27-32" . The average size is a 7.75" width and a 31" length. If your feet size are...
It doesn't matter that much, it really depends on what you are more comfortable with. So just try different sizes of skate decks at your nearest skate shop of they let you ;)