Concrete Block (CMU) Calculator
Enter the wall length, height and openings, then choose the block face size.
How it works
Blocks per sq ft = 144 ÷ (nominal face length × height in inches); an 8 × 16 in block covers 8/9 sq ft, so 1.125 per sq ft. Blocks = net wall area × blocks per sq ft × (1 + waste), rounded up. Mortar ≈ 8.5 cu ft per 100 sq ft of 8 × 16 wall. Bags = blocks ÷ blocks per bag, rounded up.
Worked example: CMHA TEK 04-02A: 100 sq ft of wall × 1.125 = 112.5 blocks, + 5% = 119. Mortar about 8.5 cu ft (TEK 03-11); at 16 blocks per 80 lb preblended bag, 8 bags.
Assumptions
- Nominal sizes include a ⅜ in joint (an 8 × 16 block is about 7⅝ × 15⅝ in). CMHA TEK 04-02A gives 119 units per 100 sq ft for 8 × 16 block including about 5% waste; that is the default here.
- Mortar is CMHA's rule of thumb from TEK 03-11: about 8.5 cu ft per 100 sq ft, with ⅜ in joints, face-shell bedding and 10% waste included. Bags use TEK 04-02A Table 2: one 80 lb bag of preblended mortar lays about 16 conventional units. Your mortar's bag yield may differ.
- Single-wythe wall. Corner, bond-beam and pilaster units, reinforcement and grout for filled cores are not counted.
- This is a quantity estimate only, not a structural or foundation design. Wall type, reinforcement and mortar type are set by local codes; check local codes and use a qualified mason or engineer where required.
Frequently asked questions
How many concrete blocks per square foot?
1.125 for standard 8 × 16 in block, because each covers 8/9 sq ft of wall. CMHA TEK 04-02A rounds that to 119 per 100 sq ft including about 5% waste.
How much mortar for a block wall?
CMHA's TEK 03-11 rule of thumb is about 8.5 cu ft of mortar per 100 sq ft of wall, including 10% waste, with ⅜ in face-shell joints.
How many blocks does a bag of mortar lay?
TEK 04-02A estimates about 16 conventional blocks per 80 lb bag of preblended mortar. Check the yield on your bag.
Related calculators
- Brick and mortar calculator
- Retaining wall block calculator
- Concrete calculator (bags and cubic yards)
- Concrete slab and pad calculator
Sources
Formulas and reference values are from these sources. Page content last updated 2026-10-19.