How to Calculate Masonry Blocks Needed to Build a House

One of the most important aspects of the building process is estimating the materials needed to complete the project.

The reason this step is so important is simple: Too many materials means the project can go over budget, and too little materials means the project can be delayed waiting on deliveries. One of the easiest items to estimate is concrete block. Whether estimating for a foundation or the entire home, it's a fairly straightforward process, but if it's not done properly, it can shut down a work site until more blocks are delivered.

Determine what kind of blocks will be used. This information can be found on the drawing. The block size helps to determine the thickness of the wall. Blocks come in many sizes, but the most common is 8 inches tall, 8 inches thick and 16 inches long.

Determine the total square footage for each wall. Use simple math to get this information: basic length times height. For this example, the house will be a simple square, 10 feet on each side with 10-foot-high walls. The total square footage for each wall is 10 feet times 10 feet, or 100 square feet.

Add up the square footage for each wall. For this example, each wall is 100 square feet, so the total square footage is 400.

Determine the square footage covered by one block. Multiply the length of the block times the height of the block--16 inches by 8 inches equals 128 square inches. Now divide the total square inches of the block by 144--128 square inches divided by 144 equals 0.88 square feet.

Determine the number of blocks needed to complete the building. Take the total square footage of all the walls and divide it by the number found in step 4. For this example, 400 square feet is divided by 0.88, which equals 454.54. If the answer has a decimal, round up to the next whole number. This number is the number of blocks needed to build the building.

Add 10 percent to the number found in step 5. To do this, multiply the rounded-up number of blocks from step 5 by 1.1. For this example, 455 times 1.1 equals 500.5. As with the previous step, round decimals up to the next whole number, so the total number of blocks is 501. This number will give enough for any breakage or unusable blocks that come in the order.

Things You Will Need

  • Architectural drawings
  • Calculator

Tip

  • Don't forget to ask for corner blocks.

Warnings

  • Double check your work.
  • Take your estimate and drawings to the block supplier if you have any questions.

About the Author

Michael Rippetoe has been writing for 15 years, and has recently decided to make it his career. He has been a journeyman carpenter, ASE Master Mechanic, certified irrigation professional and currently writes for this site, designs websites, and does professional photography. Rippetoe's articles appear on eHow, Garden Guides, AnswerBag and others.