Concrete Block Wall Calculator
Estimate concrete blocks and mortar bags for a wall from its length, height and block size.
How it works
wall area = length × height · blocks = ceil(wall area ÷ face area × (1 + waste%)) · mortar bags = ceil(blocks ÷ 33.3)
Each concrete block covers a fixed area of the wall face including its mortar joint — about 0.888 ft² for a standard 16 × 8 in block and 0.667 ft² for a 12 × 8 in unit. Dividing the wall area by that face coverage and rounding up gives the block count, and one 80 lb bag of mortar sets roughly 33 blocks. The waste allowance covers breakage, cuts around openings and the odd bad block.
Worked example
A 20 ft long, 8 ft high wall is 160 ft². Using standard 16 × 8 in blocks (0.888 ft² each) with 5% waste: 160 ÷ 0.888 × 1.05 ≈ 189.2, rounded up to 190 blocks. Mortar: 190 ÷ 33.3 ≈ 5.7, so 6 bags.
Frequently asked questions
How many blocks are in a bag of mortar?
A standard 80 lb bag of mortar mix lays roughly 33 standard blocks. Type S mortar is the usual choice for load-bearing and below-grade block; confirm the mix and coverage on the bag, since it varies with joint thickness and mason technique.
Do I need rebar and grout in the cores?
Most codes require vertical rebar grouted into the block cores at set spacing, plus horizontal reinforcing, especially for retaining or seismic walls. Rebar and core grout are separate from the block and mortar counts here — size them from your engineered plan.
How much waste should I add?
Five percent is typical for a plain wall. Add more where there are many openings, corners or a bond pattern that needs cut blocks, since each cut can leave an unusable offcut.
Related calculators
Estimate for planning. Add a waste margin and confirm with your supplier and local codes.