Concrete Block Calculator
Work out how many concrete masonry units (CMU) you need for any wall run or foundation before placing your order. Enter your wall dimensions below to calculate gross units, scrap allowance, and initial material cost.
Enter wall dimensions for quantity and a unit price for cost. Waste is optional; blank means 0%.
Total linear length of the wall or footing run.
Vertical elevation from the top of footing to cap.
Standard modular CMU dimensions account for a standard 3/8-inch mortar joint.
Recommended 5–10% for end cuts, half-blocks, and corner breakage.
Average local retail price per concrete unit.
Block face area rule:
The installed 8 × 16 in face covers exactly 8/9 ft² (0.08258048 m²), requiring 1.125 blocks/ft². Metric mode converts this same 203.2 × 406.4 mm module; it does not assume a 200 × 400 mm product. Thickness does not change face coverage.
Enter wall length and height to calculate quantities.
Waste is applied to the unrounded wall requirement, then the total is rounded up once. Net is the rounded no-waste baseline; extra blocks are the difference.
Enter your supplier’s price; cost is pending until a price is entered.
Note: Local masonry yard prices and contractor installation costs vary by area. Estimates exclude foundation footings, rebar reinforcement, core grout, mortar, labor, tax and delivery fees.
This calculator rounds to whole pieces, not full pallets. Confirm your supplier’s product coverage, pallet quantities and minimum order before purchasing.
How to use & worked block example
Choose feet or meters and enter the total wall length and height, waste and price per block. The calculation uses gross rectangular wall area; it does not deduct door or window openings. Match the actual supplier module before ordering.
24 × 6 ft (7.3152 × 1.8288 m) gives 162 raw blocks. With 10% waste, 178.2 rounds once to 179 blocks: 162 baseline plus 17 extra. At $2.85 each, the material estimate is $510.15 in both modes. USD and price per piece do not change when units switch.
How standard block calculations work
Concrete masonry relies on exact modular geometry. When calculating block counts for a foundation, stem wall, or garden partition, you convert gross wall area into block units, factor the joint spacing, and reserve independent allocations for grout and steel.
The 1.125 multiplier rule
In United States residential and light commercial construction, standard concrete blocks are manufactured 3/8-inch undersized in all three dimensions (7-5/8 inches tall by 15-5/8 inches long). Once placed in a mortar bed with standard 3/8-inch horizontal and vertical joints, each block occupies an exact footprint of 8 inches high by 16 inches long on the wall face. The exact face area is (8 × 16)/144 = 8/9 square feet, or 0.08258048 square meters. Dividing wall area by that module gives 1.125 blocks per square foot.
Standard CMU coverage
112.5 BLOCKS / 100 SQ FT
Nominal 8×8×16-inch blocks measure 7-5/8 × 7-5/8 × 15-5/8 inches. With the nominal installed joint, the face covers exactly 8/9 ft² (0.08258048 m²). Metric mode uses this converted US module.
Mortar requirements
VERIFY SUPPLIER YIELD
Mortar yield depends on the product, unit geometry and joint placement. Follow manufacturer mixing instructions and your project specification; mortar is not calculated here.
Cutting and breakage allowance
5% TO 10% ORDER BUFFER
Add 5% for simple straight retaining walls, or 10% for designs with multiple corners, openings, bond beams, and half-blocks.
Structural core filling
CORES & REBAR BUDGETED SEPARATELY
Hollow cells requiring vertical reinforcement steel and coarse grout must be calculated by internal volume, not block count.
Plan structural materials separately from blocks
Calculators estimate the physical blocks needed for the wall face. High-lift or low-lift core-fill grout, Type S mortar bags, clean washed masonry sand, and steel rebar grids must be ordered according to your local retaining or foundation wall engineering schedule.