Concrete Block Wall Calculator
Enter the wall length and height, pick your block size and mortar joint, and get the total block count, mortar volume, and how many bags of cement and sand to buy - plus a to-scale wall diagram. Nothing uploaded.
Wall Dimensions
Build Options
Results
CMU blocks and mortar calculation
How block count and mortar volume are calculated
The calculator divides wall area by block area, then adds a waste factor (typically 5-10% for breakage and cuts during installation). For mortar, it calculates the volume of each bed joint (horizontal) and perpendicular joint (vertical) based on block dimensions and joint width. A standard 10mm joint uses more mortar than a 8mm joint. This calculator shows the total mortar volume needed, then converts it to bags of cement and sand based on a 1:5 ratio (1 part cement to 5 parts sand by volume), which is standard for block laying.
Bond patterns and structural strength
Running bond (half-lap offset) is the strongest and most common pattern because blocks on upper courses rest on multiple blocks below, distributing weight evenly. Stack bond aligns all vertical joints, which looks cleaner but is weaker and needs extra reinforcement. Flemish bond alternates headers (short side showing) and stretchers (long side showing) and is primarily decorative - it's stronger than stack but less efficient than running bond.
FAQ
Why does the calculator show a coursing note?
The height must divide evenly by block height plus mortar joint for a professional appearance. If your wall height doesn't divide evenly, the calculator shows how many courses you'll have and whether you need a partial block at the top to reach your target height exactly.
What's the difference between CMU and regular bricks?
Concrete Masonry Units (CMUs) are hollow concrete blocks, typically 8x8x16 inches (203x203x406mm). Bricks are solid clay and much smaller. CMU walls are faster to build, use less mortar per block, and are cheaper - but bricks are more attractive and more durable in freeze-thaw climates.
How much waste factor should I add?
5% waste is typical for experienced masons in ideal conditions. Add 10% if it's your first wall, the wall has many corners, or you're using salvaged old blocks which break more easily. Underestimating means a mid-project supply run.