Concrete Block Calculator
Work out how many concrete blocks a wall needs at the nominal block size.
Last reviewed September 19, 2026
Result
Enter wall length and wall height to see the result.
https://calcgallery.com/masonry/concrete-block-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use it
- Measure the wall length and height.
- Enter the total area of any openings so they come out of the count.
- Check the block face size. The nominal size already includes the mortar joint.
- Read the block count.
How it is calculated
The nominal block face already contains the mortar joint, so unlike brick there is no separate joint to add:
Blocks per area = 1 ÷ (face length × face height)
Blocks = ceil(net wall area × that × (1 + waste))A standard 16 by 8 in nominal block works out to exactly 1.125 blocks per square foot, which is the figure most masons carry in their head. This calculates it from the dimensions rather than assuming it, so a different block size gives the right answer without anyone having to remember a new number.
Net wall area is the wall minus any openings.
Practical tips
Design to the module if you can. Block walls work in 8 in vertical and 16 in horizontal steps. A wall 8 ft 4 in long means cutting every other course. Moving it to 8 ft or 9 ft 4 in means cutting almost nothing.
Cut blocks are slow and noisy. Each one is a saw, a mask and several minutes. On a wall with two openings that is most of a day. It is worth an hour of planning to avoid.
Stack the blocks near the wall before you start. A standard block is heavy and you will handle each one at least twice. Moving the pallet close before laying saves more effort than any other single decision.
Fill cores as the schedule says, not as it looks right. Which cores get grout and rebar comes from a drawing. Filling more than specified wastes material; filling fewer is a structural defect.
Anything load-bearing or retaining is engineering. Height limits, footing sizes and reinforcement for block walls are regulated and vary by jurisdiction. This counts blocks. Check the rest with your building department or an engineer.
With your numbers
- Each block covers 16 in × 8 in, joint included
- Wall = 200 ft², so 225 blocks
- With 5% waste = 237 blocks
Quick reference
Blocks at openings and corners get cut, and some arrive chipped, so this includes 5% extra.
| Job | Blocks to buy |
|---|---|
| 20 × 8 ft wall | 189 |
| 20 × 10 ft wall | 237 |
| 30 × 8 ft wall | 284 |
| 40 × 8 ft wall with a 32 ft² door | 341 |
| 6 × 2.4 m wall | 184 |
| 10 × 2.4 m wall | 306 |
| 12 × 3 m wall with a 3 m² opening | 420 |
Common questions
- How many blocks per square foot?
- 1.125 for a standard 16 by 8 in nominal block. That is 200 ft² of wall to 225 blocks, before any waste allowance.
- Why is the block 15.625 inches, not 16?
- Because the nominal size includes the 3/8 in mortar joint. A block that measured a full 16 in would leave no room for mortar and the courses would not line up with anything else dimensioned in modules of 8 in.
- Do I need to subtract openings?
- Yes, and there is a field for it. A garage wall with a door in it can be a quarter opening, and ignoring that buys a lot of blocks you do not need.
- How much mortar do I need?
- This does not estimate it. Mortar quantity depends on the joint thickness, whether you are laying full or face-shell bedding, and how much you drop. Your supplier will have a figure for the block you are buying.
- What about rebar and grout?
- Not estimated here. Reinforced block walls have cores filled to a schedule that comes from a drawing, not a rule of thumb, and getting that wrong is a structural problem rather than a shopping one.
- Does this work for UK dense concrete blocks?
- The maths does, but the default size is the US 16 by 8 in nominal block. UK blocks are commonly 440 by 215 mm, so enter those dimensions and the count follows.