Concrete Block Calculator
This concrete block calculator works out how many cinder or concrete blocks you need for a wall, plus an estimate of the mortar. As a concrete block wall calculator it takes the wall length and height and the block size, then returns the total block count, the blocks per course, and the number of courses — everything you need to order materials.
How to use this calculator
- Enter the wall length and height.
- Set the block face size — the default 16 × 8 inches is the standard nominal block.
- Read the total block count and the blocks-per-course breakdown.
- Use the mortar estimate as a starting point and round up when ordering.
The formula
Divide the wall area by the face area of one block (including its mortar joint). A nominal 16 × 8 inch block covers about 0.89 ft², so a wall needs roughly 1.125 blocks per square foot:
Blocks = Wall area (ft²) ÷ Block face area (ft²)
Worked example. A 20 ft × 8 ft wall is 160 square feet. With 16 × 8 inch blocks (0.89 ft² each) that is 160 ÷ 0.89 ≈ 180 blocks — 15 blocks per course across 12 courses — and about 6 bags of mortar.
Frequently asked questions
How many concrete blocks do I need for a wall?
Find the wall area (length × height) and divide by the face area of one block. A standard 16 × 8 inch block covers about 0.89 ft² with its mortar joint, so a wall needs roughly 1.125 blocks per square foot.
How many concrete blocks are in a square foot?
About 1.125 standard 8 × 8 × 16 inch blocks per square foot of wall, once the mortar joints are included.
How much mortar do I need for a block wall?
Plan on about 3 bags of mortar per 100 blocks, plus sand. Tall walls, wide joints, and rough blocks push that number higher.
What is the actual size of a cinder block?
A nominal 8 × 8 × 16 inch block actually measures 7⅝ × 7⅝ × 15⅝ inches. The missing ⅜ inch on each face is taken up by the mortar joint, which is why calculators use the nominal size.