Concrete is a composite material of cement, aggregate materials (rocks, gravel, or similar objects), and water. Other materials are sometimes added to alter the properties of the concrete. These materials could potentially alter the color, strength, or chemical resistance of the concrete. Concrete has a density of approximately 145 pounds per cubic foot. The weight of concrete per square foot is dependent on the depth of the concrete slab.

Measure the depth of the concrete slab in inches. You may need to dig a small hole along the edge of the slab to do this if it is buried in the ground.

Divide the depth of the concrete by 12. This gives the depth of the concrete in feet.

Divide 145 pounds per cubic feet by the depth of the concrete slab. This is the pounds per square foot for the concrete.

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The recipe used to make concrete can vary significantly. A density of 145 pounds per cubic foot is a reasonable approximation for any commonly used concrete recipe.

Reinforced concrete has steel bars called rebar inserted into it. Steel has a much higher density than concrete, which causes reinforced concrete to have a higher density. A reasonable estimate of the density of reinforced concrete is 150 pounds per cubic foot. This should be substituted for the 145 pounds per cubic meter estimate for regular concrete when calculating the weight of reinforced concrete.