When needing to calculate an object's mass by its volume, or vice versa, you need to know the density of the object's material. The equation for volume in relation to mass is volume = mass / density. The equation can be altered to solve for any of the three properties, and rearranging it for mass results in mass = volume * density. With the volume dimensions given in feet, the tonnage of an object can be calculated through by using its density with comparable measurements, such as cubic feet per pound.

Measure the dimensions of the material in feet and multiply them together to determine the volume in cubic feet. For this example, the length measurement is 50 feet, the width is 20 feet and the height is 30 feet, which multiplied together equals 30,000 cubic feet.

Find the density of the material from a source like the K-Tek table of data (see Resources), and multiply the density by the volume. For this example, the material is donut mix, which has a density 40 pounds per cubic foot (lbs./ft^3). Multiplying the density of 40 lbs./ft^3 m by the volume of 30,000 cubic feet results in 1,200,000 pounds.

Divide the weight in pounds by 2,000 to calculate the equivalent weight in tons. For this example, 1,200,000 pounds divided by 2,000 results in 600 tons.