Everybody have the six packs wether he/she ever workout or not , big or small isn't the issue , it's about how much fat is covering it.
Generaly , for males you must get below the 10% to have visible abs , and it's 15% for females , as "3rd_degreeburn" pointed out .
However , if you have very big ab muscle (gained by very hard training) , it could be barely visible at a little higher than the 10% .

3rd_degreeburn - It's great to find somebody else who pumps iron on this forum ... Do you still workout ?