The density of concrete varies, depending on the density of the aggregate used to mix the concrete and the amount of air within it. Floors, bridges and other structural components use high-density concrete, while low-density concrete works in areas with harsh weather and in some roads. The formula for calculating density is density equals mass divided by volume. Pounds per cubic feet are the typical unit for measuring concrete density.
Use an angle grinder equipped with a masonry blade to trim your concrete sample into a rectangular or square shape if it isn't already rectangular or square. This facilitates quick volume calculations.
Weigh the sample on the scale to calculate its mass in pounds.
Measure the length, width and height of the sample in inches. Calculate the volume of the concrete by multiplying length, width and height together. This will give you the volume in cubic inches.
Convert the volume in cubic inches to the volume in cubic feet by dividing the volume in cubic inches by 1,728. Say your sample is 3 inches by 3 inches by 3 inches. Multiply the length, width and height and the volume is 27 cubic inches. Since there are 1,728 cubic inches in a cubic foot, you divide 27 by 1,728 to come up with a volume of 0.015625 cubic feet for the sample.
Divide the weight of the concrete by the volume to calculate the density. If the sample weighs 2 1/4 lbs. and the volume is 0.015625 cubic feet, the density of the concrete would be 144 lbs. per cubic foot, which is right in line for concrete.