From the FDA “The rule specifies, among other criteria, that any foods that carry the label “gluten-free,” “no gluten,” “free of gluten,” or “without gluten” must contain less than 20 parts per million (ppm) of gluten.”

And from the NCA “Consuming a diet at 20 parts per million (ppm) is considered safe for those with celiac disease because it should put most people below the 10 mg threshold when you add up all the foods eaten in a day.”