Technically.... none. A slug is a measurement of mass, not weight and thus comparing ounces to slugs is like comparing pumpkins to rutabagas.

But if you insist on muddying the waters, there would be about 512 ounces in a slug, a slug being the amount of mass that would accelerate at one foot per second per second with an application of one lb-ft of force, making it sort of the equivalent of one pound acted upon by the force of gravity which would impart a force of 32 pounds.

tanstaafl.