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— Gravel Quantity equals Gravel Volume. For a Class "A" mix, the gravel multiplier is 0.90m3 * 1 = 0.90m3. Photo Courtesy: Pixabay. Sample Problem #2. Calculate the amount of 50kg cement bags, sand, and gravel required for a 5 meter long, 10 meter wide, and 0.250 meter thick class "C" mixed slab. Solution #2