Concrete Block Calculator
Concrete masonry units (CMU) are the backbone of foundation walls, retaining walls, and commercial construction. This calculator determines the exact number of blocks needed for your wall dimensions, accounting for openings like doors and windows, plus mortar bags and an approximate material cost.
Standard CMU blocks measure 8" high x 16" long (including a 3/8" mortar joint, the nominal size is 8" x 8" x 16" even though actual dimensions are 7-5/8" x 7-5/8" x 15-5/8"). This means each block with its mortar joint covers 0.889 square feet of wall face, or about 1.125 blocks per square foot.
The calculator includes a 5% waste factor for cuts, breakage, and on-site damage. For walls with many openings or complex shapes, consider increasing the waste allowance. Corner blocks, half blocks, and lintel blocks are specialty items. Order these separately based on your plan details.
Mortar coverage is approximately 33 standard blocks per 80-lb bag of pre-mixed mortar with 3/8-inch joints. For 12-inch blocks, you'll use slightly more mortar per block due to the wider bed joint. Always have extra mortar on hand; running out mid-course is far worse than having a few bags left over.