To determine a frying pan's size, measure the pan's diameter from rim to rim. A frying pan's advertised size is not the diameter of the cooking surface, and due to the tapered design of a frying pan, that diameter will always be around 2 smaller.
Aluminum is lightweight but strong and doesn't warp when exposed to high heat. Since they're such good conductors of heat, aluminum frying pans are great for frying and sautéing foods. The main drawback of aluminum is that it reacts with alkaline and acidic foods. This causes corrosion and leads to leaching of the metal into the food, which acquires a metallic taste.