CMU Block Estimator
Estimation Summary
How to Calculate CMU Blocks for Your Project
Planning a masonry project requires precision to ensure you order the correct amount of material without excessive waste. CMU (Concrete Masonry Unit) blocks are typically sized nominally, which means the listed dimensions (e.g., 8″ x 8″ x 16″) include the thickness of the mortar joint, usually 3/8 of an inch.
The Math Behind the Calculation
To calculate the number of blocks needed for a wall, follow these steps:
- Step 1: Calculate Wall Surface Area. Multiply the length of the wall by the height (Length × Height = Area in square feet).
- Step 2: Determine Block Surface Area. A standard 8x8x16 block has a surface face of 8 inches by 16 inches. In square feet, this is approximately 0.89 sq. ft.
- Step 3: Divide. Divide the total wall area by the surface area of one block.
- Step 4: Account for Waste. Add 5% to 10% for cuts, breakage, and mistakes.
Standard CMU Sizes
While the 8x8x16 block is the industry standard, other sizes exist. Our calculator allows you to select different nominal heights and lengths. Remember that the "width" (thickness) of the block does not affect the face count, only the amount of concrete or grout required to fill the cells.
Example Calculation
If you have a wall that is 10 feet long and 8 feet high, your total area is 80 square feet. Using standard 8x8x16 blocks (0.888 sq. ft. per block):
80 / 0.888 = 90.09 blocks.
With a 10% waste factor, you would order approximately 100 blocks to be safe.
Important Considerations
When using this CMU block calculator, keep in mind that openings for windows and doors should be subtracted from your total wall area before calculating the block count. Additionally, if you are building a corner, you may need specific "corner blocks" which have finished ends, though the quantity calculation remains largely the same.