A density of pounds per cubic foot is a measure of the relationship between weight and volume of an item.

As an example, a cord of firewood measures 8 feet * 4 feet * 4 feet with a volume of 128 cubic feet (ft³). The weight of this pile of firewood = 2500 pounds (lb) and you would like to know the weight of one cubic foot of this firewood?

To get the density of pounds per cubic foot divide the weight in pounds by the cubic feet amount
2500 ÷ 128 = 19.53

This pile of firewood has a density of 19.53 pounds per cubic foot, or one cubic foot of firewood in this pile has a weight of 19.53 pounds