Registered. When combined, an 80-pound bag of dry concrete will weigh approximately 80 pounds. One cubic yard is equivalent to 3250 square inches and covers a surface area of about 8 square feet. A layer of one inch of concrete has a density of around 2000 lbs per cu yd or 0.5 oz/ft3. Concrete is a mixture of water and cement that can be made into any shape you like. It's used for roads, bridges, buildings, and more. When it gets wet, it becomes hard again if it's kept out of the rain, but if it's allowed to get soaked, it will dissolve away. Concrete needs to be mixed with water and cement before it can be used, and this mixing process is called "placing." The type of placing machine you use depends on how much concrete you need to mix in one go. For example, if you are making a small amount of ready-mixed concrete, such as for a patio, then you would use a hand mixer. If you were making a large amount, such as for a driveway, then you would need a truck-mounted mixer. The weight of a bag of concrete depends on how much air is inside it.