Concrete Block Calculator
Estimate concrete masonry units and optional mortar bags from wall dimensions, openings and nominal block face size.
How it works
Wall area divided by nominal block face area
For a nominal 8 × 16 inch block face, one block represents about 0.889 square feet of wall before extra material is added.
Bond patterns, half blocks, corners, lintels, reinforcing, grout and structural details are not included.
Why use nominal dimensions?
Nominal masonry dimensions typically represent the block plus its mortar-joint module. Using only the smaller actual molded dimensions can overstate block count.
Is the mortar estimate exact?
No. Mortar yield varies with joint width, block type, waste and bag size. Enter a blocks-per-bag value from your product or supplier.
Real-world project example
How many concrete blocks for a 20 ft long wall?
For a 20 ft wall that is 4 ft tall, the face area is 80 square feet. A standard nominal 8 × 8 × 16 inch CMU covers about 0.889 square feet of wall face, including nominal mortar joints. That is roughly 90 blocks before openings, cuts and waste; a 5% allowance raises it to about 95 blocks. Actual block sizes, bonds and corner details change the count.
Before you buy materials
Estimate mortar separately using manufacturer guidance. Structural walls require appropriate footing, reinforcement and local building-code review.
Adjust the measurements, waste allowance and purchase options in the calculator above to estimate your own project; examples are for planning only.