3.5 to 6.5 mm long. As in the case of many stored goods pests, adult and larva sizes can vary; they directly depend on food availability, nutrient richness and larval competition.
Elongate oval body, about 2.25-fold more in length than in width, round at the ends.
Small head, slightly protruding from the prothorax, with one median ocellus on its front.
Males and females have 11-articled antennae, the last 3 articles form a quite clearly differentiated club.
Uniform very dark brown to black. Elytra slightly less dark than pronotum. The ventral face is black and covered in downy, short, fine, greyish bristles. Attagenus pellio is easily recognisable and can easily be told from related species thanks to the presence of 3 whitish spots (2 lateral ones and 1 median one) at the base of the pronotum, and 1 in the middle of each elytron.