How to use the concrete block calculator calculator
- 1
Measure the wall face
Measure the length and height of each wall and add a section for each. For a wall that steps down a slope, treat each step as its own section rather than averaging.
- 2
Subtract openings
Doors, windows, and vents are not blocked. Reduce the area you enter, or subtract them from your dimensions before entering.
- 3
Enter the actual block size
Use the measured dimensions of the block, not the nominal size. A nominal size normally already includes the mortar joint, so entering it along with a joint counts the joint twice.
- 4
Enter the mortar joint
Enter the joint your mason is working to. The calculator adds it to both the length and the height to build the repeating module.
- 5
Add an allowance and price it
Add a percentage for cuts at openings, corners, and half blocks, then enter your price per block for an estimated total.
Formula
Blocks = wall area(sq ft) / (((block length + joint) / 12) x ((block height + joint) / 12))
Enter the actual block size with the joint separately. Entering a nominal size and a joint together double counts the mortar.
Worked example
A wall 40 feet long and 8 feet high, using blocks measuring 15.625 by 7.625 inches with a 0.375 inch joint
- 1Wall area: 40 x 8 = 320 square feet.
- 2Module size: 15.625 + 0.375 = 16 in, and 7.625 + 0.375 = 8 in.
- 3Module area: (16 / 12) x (8 / 12) = 0.8889 square feet.
- 4Blocks per square foot: 1 / 0.8889 = 1.125.
- 5Blocks for the wall: 320 / 0.8889 = 360.
The wall takes 360 blocks before any allowance. Those dimensions are the ones entered for this example, not a standard block size.
Worked examples
Counting the courses
The same 8 foot wall with a module height of 8 inches
- 1Wall height in inches: 8 x 12 = 96 in.
- 2Courses: 96 / 8 = 12 courses.
- 3Blocks per course: 40 ft x 12 = 480 in, divided by 16 in = 30.
- 4Total: 12 x 30 = 360 blocks, matching the area method.
Counting by course gives the same answer and is a useful cross-check. It also tells you whether the wall height works out to whole courses, which the area method hides.
The nominal size trap
Entering a 16 by 8 inch nominal size along with a 0.375 inch joint
- 1Module the calculator would build: 16.375 by 8.375 in.
- 2Module area: 0.9522 square feet, giving 1.05 blocks per square foot.
- 3Blocks for the 320 square foot wall: 336.
- 4Correct figure using the actual size: 360.
Double counting the joint understates this wall by 24 blocks. Enter the measured block size with the joint separate, or a nominal size with the joint left blank.
Nominal size and actual size
Concrete blocks are usually described by a nominal size that is designed to include the mortar joint, so that walls lay out on a regular grid. The actual block is smaller than its nominal description by roughly the thickness of one joint in each direction.
That convention is convenient on site and a trap in a calculator. If you enter a nominal size and then also enter a joint, the arithmetic adds the joint a second time, the module comes out too large, and the block count comes out low.
There are two correct ways to use this page. Measure the actual block and enter the joint separately, which is what the fields are labeled for. Or enter the nominal size and leave the joint blank, because the nominal figure already has the joint built in. Both give the same answer; mixing them does not.
Counting by course as a cross-check
The area method is quick, but block walls are built course by course, and counting that way catches things the area method hides. Divide the wall height by the module height to get courses, and the wall length by the module length to get blocks per course.
The useful part is what the course count tells you about the height. A wall height that does not divide evenly into whole courses means either a cut course, a different block, or a change to the wall height, and it is far better to discover that while estimating than while laying.
The two methods agree exactly when the wall divides evenly, as in the worked example. When they disagree, the course method is telling you something real about the layout.
What a block count leaves out
The count covers full blocks in the field of the wall. Real walls also need corner blocks, half blocks at openings and ends, bond beam or lintel blocks over openings, and sometimes specially shaped units at sills and caps.
Those are usually ordered separately by type rather than absorbed into the field count, because they are different products. Work out how many your drawings call for and add them to the order.
Mortar, reinforcement, grout for filled cores, wall ties, and control joints are all separate quantities as well. This calculator does not estimate any of them, and whether a wall needs filled cores or reinforcement is a structural question rather than an arithmetic one.
Common mistakes
Where block counts go wrong:
- Entering a nominal block size and a joint together, which counts the mortar twice.
- Dividing by the bare block face and ignoring the joint entirely, which counts it zero times.
- Forgetting corner, half, and bond beam blocks, which are ordered separately.
- Averaging a wall that steps down a slope instead of treating each step as a section.
- Assuming the wall height divides into whole courses without checking.
- Ordering the exact count with no allowance for breakage and cuts.
Sources and methodology
Every figure on this page comes from geometry rather than from a product database. Areas use the standard area formulas, counts divide an area by the size of one unit, and unit conversions use exact factors: 12 inches to a foot, 9 square feet to a square yard, and 100 square feet to a roofing square.
YardCalc publishes no product dimensions, coverage rates, or prices. Unit sizes differ between manufacturers and regions, and a figure that is right for one product is wrong for another, so the calculator asks you for the size of the product you are actually buying. Prices are yours alone.
Results are planning estimates, not order quantities. Read how every value on the site is derived and checked in the YardCalc calculation methodology.
Blocks per square foot by block size
Worked arithmetic at a 0.375 inch joint over a 320 square foot wall. These are calculation examples using actual block dimensions, not standard or recommended sizes.
| Unit face size | Module with joint | Units per sq ft | Units for 320 sq ft |
|---|---|---|---|
| 15.625 x 7.625 in | 16 x 8 in | 1.13 | 360 |
| 15.625 x 3.625 in | 16 x 4 in | 2.25 | 720 |
| 11.625 x 7.625 in | 12 x 8 in | 1.5 | 480 |
| 7.625 x 7.625 in | 8 x 8 in | 2.25 | 720 |
Frequently asked questions
- How many concrete blocks per square foot?
- For a block measuring 15.625 by 7.625 inches laid with a 0.375 inch joint, the module is 16 by 8 inches and the answer is 1.125 blocks per square foot. Smaller blocks need more. Enter your own dimensions above.
- How many blocks for a 10 x 10 wall?
- A 10 by 10 foot wall is 100 square feet. At 1.125 blocks per square foot that is 113 blocks before any allowance. The figure changes with your block size and joint.
- Should I use the nominal or actual block size?
- Either, but not both with a joint. Enter the actual measured size with the joint separately, or the nominal size with the joint left blank, because a nominal size already includes the mortar. Entering a nominal size plus a joint counts the mortar twice and understates the count.
- How do I count courses?
- Divide the wall height by the block height plus the joint. An 8 foot wall with an 8 inch module is 96 divided by 8, which is 12 courses. If it does not divide evenly, the layout needs attention before you start laying.
- Does this include corner and half blocks?
- No. The count covers full blocks in the field of the wall. Corner blocks, half blocks, and bond beam or lintel blocks are different products and are ordered separately from your drawings.
- Does this include mortar or grout?
- No. Mortar, and grout for filled cores, are separate estimates. Whether cores need filling at all is a structural decision, not something this calculator determines.
Block counts divide your measured wall area by the module area, which is the block size you enter plus the joint you enter. No block size, joint width, or price is assumed, and nothing here addresses structural design. Counts come from exact geometry using the product dimensions you enter. Confirm the product size, the layout, cutting and breakage, and the final order quantity with your supplier before purchasing.
Results are planning estimates. Last reviewed 2026-08-30.