Concrete Block Calculator
A 20 by 8 ft wall (160 sq ft) needs about 198 standard 8x8x16 concrete blocks at 1.125 blocks per square foot with 10% waste. Enter your wall length and height, adjust the blocks per square foot if your block size differs, set a waste percentage, and add an optional price per block to get the block count and total cost.
Quick answer
Wall area is length times height, and block count is that area times the blocks per square foot for a standard 8x8x16 CMU.
What this tells you
- •Wall area is length times height, and block count is that area times the blocks per square foot for a standard 8x8x16 CMU.
- •A standard concrete block has a 16 by 8 inch face, so one block covers about 0.89 sq ft and it takes about 1.125 blocks to cover a square foot.
- •A 10% waste factor covers cracked blocks, cuts at corners and openings, and the odd unusable block on a pallet.
How to Use
- 1Enter the wall length and height in feet.
- 2Leave blocks per square foot at 1.125 for a standard 8x8x16 CMU, or adjust it for a different block size.
- 3Set the waste percentage, usually around 10% for cracked blocks and cuts.
- 4Add an optional price per block if you want a cost estimate.
- 5Click Calculate to see the wall area and the number of blocks needed.
How It Works
Formula
Wall Area = Length x Height
Blocks = ceil(Wall Area x Blocks per sq ft x (1 + Waste%))Wall area is the face area of the wall in square feet. Multiplying by the blocks per square foot for a standard 8x8x16 CMU gives the bare block count, and the waste factor adds extra for cracked units and cuts. The result rounds up because you cannot order a fraction of a block.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Garage wall, 20 by 8 ft
Wall area is 20 x 8 = 160 sq ft. At 1.125 blocks per square foot that is 180 blocks, and a 10% waste factor brings it to 198 blocks.
Retaining wall section with cost, 12 by 8 ft
Wall area is 12 x 8 = 96 sq ft. At 1.125 blocks per square foot that is 108 blocks, and 10% waste rounds up to 119. Multiplying by the price per block gives the total cost.
Blocks per Square Foot by CMU Size
Approximate concrete blocks per square foot of wall face, including a standard mortar joint. Larger or thicker blocks change the count less than you might expect because the face size, not the thickness, drives coverage.
| Block Size (nominal) | Blocks per sq ft |
|---|---|
| 8 x 8 x 16 in (standard) | 1.125 |
| 6 x 8 x 16 in | 1.125 |
| 4 x 8 x 16 in | 1.125 |
| 8 x 4 x 16 in (half-height) | 2.25 |
How Many Concrete Blocks per Square Foot
Blocks per square foot depends on the face dimensions of the block, not its thickness. A standard concrete masonry unit (CMU) has a nominal 16 by 8 inch face including the mortar joint, which works out to about 0.89 sq ft per block, or 1.125 blocks per square foot. This figure holds for 4, 6, and 8 inch thick blocks because they share the same face size.
Half-height blocks, sometimes used for the top course of a wall or for split-face accent rows, have an 8 by 4 inch face and need about 2.25 blocks per square foot, twice the standard rate. Always match the blocks per square foot to the unit you actually plan to lay.
This calculator counts field blocks only. It does not add corner blocks, bond beam units, or rebar and grout for reinforced cells. If you also need to estimate a footing for the wall, the concrete calculator covers that part.
Common mistakes
- Assuming block thickness changes the blocks-per-square-foot rate when it is actually the face size that matters
- Forgetting the waste factor and running short near the top course
- Not counting both faces of a wall that is finished with block on two sides
- Skipping extra units for corners, which use special corner blocks not covered by a flat area count