Aluminum is approximately what fraction of the weight of steel?

Aluminum is approximately one-third the weight of steel, which is why this answer is correct. The specific gravity of aluminum is about 2.7 g/cm³, while steel typically has a specific gravity of around 7.8 g/cm³. This difference in density means that for the same volume, aluminum will weigh significantly less than steel.

Using this ratio, when one compares equal volumes of both materials, aluminum is indeed lighter, reinforcing the idea that it weighs about one-third as much as steel. This property of aluminum makes it an attractive choice in many applications, especially in the automotive industry, where weight reduction can lead to improved fuel efficiency and performance.