How to Calculate Cinder Blocks
CMU (Concrete Masonry Unit) blocks are calculated by dividing the total wall area by the face area of each block, including a 3/8 inch mortar joint. The standard 8x8x16 block has an effective face area of about 0.889 sq ft.
| Block Size | Blocks per 100 sq ft | Common Use |
|---|---|---|
| 8x8x16 (standard) | ~113 | Walls, foundations, retaining walls |
| 8x4x16 (half height) | ~225 | Decorative, low walls |
| 12x8x16 | ~113 | Load-bearing walls, below grade |
| 6x8x16 | ~113 | Interior partitions |
Frequently Asked Questions
True cinder blocks used fly ash or cinders as aggregate and are no longer manufactured. Modern CMU blocks use portland cement aggregate. The terms are used interchangeably — all blocks sold today as cinder blocks are actually concrete masonry units.
A standard pallet of 8x8x16 CMU blocks typically contains 72 blocks and weighs approximately 2,100–2,400 lbs. Always confirm with your supplier as quantities vary by manufacturer.
CMU masonry typically costs $10–$20 per square foot of wall (labor + materials). Materials alone run $3–$7/sq ft. Labor is $7–$15/sq ft depending on complexity, height, and reinforcement requirements.
Retaining walls, foundation walls, and walls over 4 feet tall typically require vertical and horizontal rebar reinforcement per local building codes. Always check with your local building department before construction.
One 60-lb bag of premixed mortar covers approximately 25 standard 8x8x16 blocks at a 3/8 inch joint thickness. This calculator estimates mortar bag requirements automatically based on your block count.
The most common CMU is nominally 8x8x16 inches (actual dimensions: 7-5/8 x 7-5/8 x 15-5/8 inches to allow for 3/8 inch mortar joints). Other common sizes: 8x4x16, 8x12x16, and 6x8x16.