Steel can be extremely strong. Aluminum is usually somewhat weaker, although the material strength of some aluminum is higher than that of some steel. The strength of materials depends on composition and the processes used to prepare them- things like heat treatment and cold working. The strength values of all types of materials are catalogued and used by engineers in the design of products. Fundamentals of Design Optimization Density is a measure of weight per unit volume.
Steel is more dense than wood, so a cubic inch of steel is heavier than a cubic inch of wood.
As area is measured in square inches, volume is measured in cubic inches. Density is therefore measured in pounds per cubic inch. Steel weighs about .28 pounds per cubic inch. Bending stress, for example, is inversely proportional to the third power of the width of a member, in the direction of bending. That is, if you made it twice as thick, you would reduce bending stress by a factor of eight.