Concrete & masonry
Concrete Block Calculator
Estimate standard CMU blocks, pallets, mortar bags, waste, and optional material cost from wall dimensions and openings.
Estimated order quantity
0 blocks to buy
- Block module
- Waste
- Mortar estimate excludes grout, reinforcement, bond beams, lintels, and footing.
Planning estimate only. Verify product specifications, site conditions, and supplier purchase increments before ordering.
How the concrete block estimate works
Gross wall area is length × height. Openings are subtracted, then the net area is divided by the nominal block face area. A standard 8 × 8 × 16 in CMU occupies a modular face of 128 in² including the 3/8-inch mortar joint, so it takes 1.125 blocks per square foot, or 112.5 blocks per 100 ft² before waste.
Order blocks: round up(net blocks × (1 + waste))
Mortar bags: round up(order blocks ÷ entered bag yield)
Nominal and actual CMU dimensions
CMHA explains that standard CMU nominal dimensions include the mortar module. An 8 × 8 × 16 in unit is typically 3/8 in smaller in each specified dimension so a 3/8-inch joint preserves the 8-inch module. Using the smaller actual face dimensions for wall coverage would double-count the joint.
Worked example
A 20 × 8 ft wall has 160 ft². Standard 8 × 16 in modular blocks require 180 units before waste. With 10% waste, buy 198 blocks. At 13 standard blocks per 80 lb mortar bag, plan for 16 bags. If the supplier packs 90 blocks per pallet, that is two full pallets plus 18 loose blocks.
Before ordering
- Confirm unit size, shapes, colors, pallet quantities, and mortar yield with the supplier.
- Estimate corner, bond-beam, lintel, sash, half, and cap units separately from standard stretcher blocks.
- Structural walls require project-specific design, reinforcement, grout, footing, drainage, flashing, and code review.
- Do not subtract small openings without considering cuts and layout around them.
Technical references: CMHA concrete masonry unit sizes and specifications, ASTM C90, and QUIKRETE Mason Mix data sheet.
Concrete block calculator FAQ
How many 8 × 8 × 16 blocks cover 100 square feet?
The modular calculation is 112.5 blocks before waste, so at least 113 whole blocks. Ten percent waste raises the purchase quantity to 124 blocks.
Why is the result not 128 blocks per 100 square feet?
128 is the nominal face area of one standard block in square inches. Since one square foot has 144 square inches, the correct modular rate is 144 ÷ 128 = 1.125 blocks per square foot.
Does this include mortar?
Yes, as whole 80 lb bags using an editable blocks-per-bag yield. Confirm the current product data sheet and job conditions.
Does it include grout or rebar?
No. Grout, reinforcement, lintels, bond beams, footing, drainage, and specialty units are separate project-specific estimates.