How Much Concrete for a 10'' Block?

Dimensions

• To begin, convert the length, width and height of the concrete block from inches to feet. If the block is 10 inches by 6 inches by 3 inches, for example, you would divide each of these values by 12, since there are 12 inches in a foot, which gives you 0.833 feet times 0.5 feet times 0.25 feet. Next, multiply the length of the concrete block times its width times its height. A block with dimensions of 0.833 times 0.5 times 0.25 has a volume of 0.104 cubic feet.

Yards

• Amounts of concrete are usually measured and sold in cubic yards, so divide your results by 27 to obtain the number of cubic yards. If you have 0.104 cubic feet, for example, you should divide by 27 to obtain 0.004 cubic yards. The density of concrete is typically close to 145 pounds per cubic foot, so this block would require a little over 15 pounds of concrete. Home improvement stores sell premix bags in a range of sizes, with 40, 60 and 80 pounds are the most common; a 40-pound bag gives you a little over 2 ½ blocks of this size. It's also an excellent idea to order a little more than you need to make sure you don't run out. You can do so by adding 5 percent to the total volume you calculate or by adding 1/4 inch to the height of your block.

Weight

• Although quantities of concrete are usually measured in terms of their volume, the weight is of course an extremely important consideration. Very large quantities of concrete will be very heavy and very difficult to move. A cubic yard of concrete, for example, weighs nearly 2 tons. If the amount of concrete you need is close to or exceeds a cubic yard, it's probably better to order ready mix rather than mixing your own, because the challenges involved in working with two tons of material may be significant.

Considerations

• If you're working with a small amount of concrete, you can buy bags of premix if you prefer. Bags of premix will generally indicate how much water you should add and what kind of volume of concrete you will get from each. The weight of the bags varies depending on the outlet and their products. Home improvement stores may also sell different types with various additives; check with your local home improvement store to see what they stock.