The average slice of wheat bread contains about 4.8 grams of gluten, which is slightly less than 5,000 mg of gluten. Regular processed white bread can contain around 12,400 mg or 124,000 ppm of gluten, but the usual slice runs around 3,515 mg (35,150 ppm) of gluten. Gluten free bread, on the other hand, will contain less than 20 ppm.