Concrete Block Calculator

About this calculator

Standard concrete masonry units (CMUs) measure 8×8×16 inches nominal, and estimating how many you need for a wall starts with dividing the wall’s area by the face area each block covers once its ⅜-inch mortar joints are accounted for — this calculator then adds a standard 5% waste factor to cover cut blocks, breakage, and layout adjustments around corners and openings, which is the margin contractors routinely build into material takeoffs.

Contractors and DIY builders use this calculation before placing a materials order, since under-ordering means a mid-project supply run (and risking a slightly different batch/shade of block) while over-ordering ties up cash in blocks that may not get used. It’s a standard first step in masonry estimating alongside separate mortar and rebar takeoffs, and it scales directly with wall length and height, making it easy to re-run for a revised wall design.