Changing tons of asphalt into an equivalent volume will let you know what space it will cover in cubic feet. Knowing the coverage volume of asphalt will save you trips to the store if you buy the correct tonnage initially. Achieve the conversion of asphalt tonnage by use of the material's weight density. Weight density measures the compactness of a substance. For example, standard asphalt has a weight density of 145 lb. per cubic foot. The volume of a space depends on its physical dimensions.
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Multiply the number of tons of asphalt by 2,000 to convert to a weight in pounds. For example, 4.2 tons of asphalt results in 4.2 tons times 2,000 lb. per ton, or a weight of 8,400 lb.

Divide the asphalt weight by its weight density, in pounds per cubic foot, to arrive coverage volume in cubic feet. Performing this step leads to 8,400 lb. divided by 145 lb. per cubic foot, or a volume of 57.9 cubic feet.

Divide the volume by 27 to convert to cubic yards, because a single cubic yards equals 27 cubic feet. Completing the example, you have 57.9 cubic feet divided by 27 cubic feet per cubic yard, or a coverage volume of 2.1 cubic yards.
References
 Georgia State University: Density
 "Physics for Scientists and Engineers With Modern Physics"; Raymond A. Serway, et al.; 2009
 Engineering ToolBox: Volume Units
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