Concrete Block Calculator
CMU blocks, mortar bags and cost for a wall with openings.
How it works
Net wall area is gross length × height minus openings. It is divided by the nominal block module face, which includes the mortar joint, then the allowance is added and the result is rounded up to whole CMUs.
The standard preset uses an 8 × 16 in nominal face. Actual block dimensions are commonly 3/8 in smaller so a 3/8 in joint completes the module. Mortar yield is product-specific and editable. Grout, bond beams, reinforcement and structural design are outside this quantity estimate.
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How the Concrete Block Calculator works
This concrete block calculator estimates CMUs and mortar bags for a wall after subtracting doors and windows. It uses nominal US module dimensions, rounds to whole blocks and can price both block and mortar quantities.
Count the nominal module, not the bare block face
A standard 8 × 8 × 16 in CMU has a nominal face module of 8 × 16 in including one mortar joint. CMHA notes that specified unit dimensions are commonly 3/8 in smaller, allowing a 3/8 in joint to complete the module. Entering the actual 7⅝ × 15⅝ in face without the joint overstates the count.
The calculator subtracts opening area, divides by the nominal module, applies the allowance and rounds up. A 100 ft² wall uses 112.5 standard modules before waste, or 119 blocks at a 5% allowance.
Mortar yield is a product input
The default of 12 standard 8 in blocks per 80 lb bag follows Sakrete's current Type S Mortar Mix yield. Bag size, joint geometry, bedding method and site loss change that figure, so replace it with the selected product data sheet.
This page is a material-count tool, not a structural wall design. Cell grout, reinforcement, bond beams, lintels, control joints, footing design and labor depend on the specified assembly and are intentionally excluded from the total.
FAQ
How many 8 × 8 × 16 blocks are needed for 100 sq ft? expand_more
The nominal module gives 112.5 blocks before waste. Add 5% and round up to 119 blocks, matching CMHA's published estimating example.
Should I enter the actual 7⅝ × 15⅝ in block size? expand_more
Not for a standard modular layout. Enter the nominal 8 × 16 in face because the actual unit plus its typical 3/8 in mortar joint completes that module.
Does the estimate include grout and rebar? expand_more
No. Cell grout, reinforcement, bond beams and lintels depend on the structural design and must be estimated from the specified wall assembly.