Concrete Block Calculator: Block, Mortar and Grout
Wall length, height, block width and how many cells get grouted, and it returns the block count, the mortar bags, the grout in cubic feet and yards, the vertical steel and the joint reinforcement. The grout line is the one that decides whether you are mixing in a wheelbarrow or ordering a truck.
When the figures look right, the block material list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
Worked example
These are the figures the calculator opens with and the answer it gives. Change anything above and every number below moves with it.
- Wall length40 ft
- Wall height8 ft
- Openings to deduct0 sq ft
- Block width, nominal8 in
- Grouted cellsEvery 48 in
- Waste allowance5 %
Block to buy378 block
| Net wall area | 320 sq ft |
|---|---|
| Block before waste | 3601.125 per sq ft |
| Courses | 1230 block per course |
| Mortar to buy | 16.6 cu ft |
| Mortar mix, 80 lb bags | 2813 block per bag |
| Cells to grout | 11 |
| Grout | 16.5 cu ft0.61 cu yd |
| Vertical rebar | 110 ft11 bars at 48 in on center, wall height plus a 2 ft lap |
| Joint reinforcement | 240 ftevery other course |
The material list this produces
| Block | 378 |
|---|---|
| Mortar mix, 80 lb bags | 28 |
| Grout, cu yd | 1 |
| Vertical rebar, ft | 110 |
| Joint reinforcement, ft | 240 |
What this calculator assumes
- Every block here is 8 by 16 nominal on the face, which is the standard unit whatever its width. That works out to 1.125 blocks per square foot of wall, and the figure already contains the 3/8 mortar joint.
- Mortar is the bed and head joints across the face shells, multiplied by 3.6. The multiplier lands the bag count on the coverage printed on the bag, where an 80 pound bag of mortar mix yields about 0.6 cubic feet and lays roughly 13 standard block.
- Grout volume uses the cell section for the block width: about 27 square inches for an 8 inch block, less for a 4 or 6 and more for a 10 or 12. Fully grouting an 8 inch wall works out near 0.28 cubic feet per square foot of wall, which is the figure the block industry publishes.
- Vertical bars are one per grouted cell. On a fully grouted wall they are figured at 48 inches on center instead, because grouting every cell does not mean putting a bar in every cell.
- Horizontal joint reinforcement is every other course, which is 16 inches.
1.125 block per square foot, and where the number comes from
Every standard concrete block is 8 by 16 nominal on the face whatever its width, which is 15 5/8 by 7 5/8 actual plus a 3/8 joint. One block occupies 128 square inches, which is 0.888 square feet, which is 1.125 blocks per square foot of wall.
That is the whole calculation, and it does not change between a 4 inch block and a 12 inch block. Width changes the mortar, the grout and the weight on the pallet. It does not change the count.
A 40 by 8 foot wall is 320 square feet, so 360 block bare and 378 with 5 percent waste. Twelve courses at 8 inches each, 30 block to a course at 16 inches each, and the two multiply back to the same 360.
Mortar for block is not mortar for brick
Block is mortared on the face shells only, not across the full width, so a 12 inch block does not take three times the mortar of a 4 inch one. That 40 by 8 wall in 8 inch block takes 28 of the 80 pound bags, and the same wall in 12 inch block takes 34.
Twenty eight bags for 360 block is 13 block a bag, which is the coverage printed on a bag of type S or type N mix. If your count and the bag disagree by much, one of them is wrong, and it is usually a wall that is being mortared full bed when it should be face shell bedded.
Full bed mortar belongs at the base course, on a solid unit, and anywhere the drawing calls for it. Everywhere else face shell bedding is the standard, and it is what the bag coverage assumes.
Grout is the line that decides the pour
Grouting every 48 inches on that 40 foot wall is 11 cells and 16.5 cubic feet. Tighten to every 32 inches and it is 16 cells and 24 cubic feet. Neither is a truck. Both are a mixer and a morning.
Solid grouting is a different job. A 24 by 8 foot wall fully grouted in 8 inch block is 54 cubic feet, which is two cubic yards, and at that point you are ordering grout rather than mixing it. Fully grouting an 8 inch wall works out near 0.28 cubic feet per square foot, which is the figure the block industry publishes.
Block width drives it hard. The same 11 cells at 48 inches is 16.5 cubic feet in 8 inch block and 28.7 in 12 inch, because the cell section nearly doubles. Decide the width and the fill together, because they multiply.
Courses land on 8 inches, so plan the height around it
Eight foot of wall is exactly 12 courses and that is not a coincidence, it is why the block is 8 inches nominal. Every dimension on a block job wants to land on a multiple of 8 vertically and 16 horizontally, and the ones that do not get cut.
The same applies sideways. A 40 foot wall is 30 whole blocks a course. A 41 foot wall is 30 blocks and a cut at every single course, twelve cuts that buy you one foot.
Joint reinforcement goes in every other course, so 6 of the 12 courses on that wall, which is 240 feet of ladder or truss wire. It is cheap, it goes in as you lay, and it is the crack control that a block wall otherwise does not have.
Questions people ask
How many blocks do I need for a 40 by 8 foot wall?
360 bare and 378 with 5 percent waste. The wall is 320 square feet and concrete block runs 1.125 to the square foot, which is 12 courses of 30 blocks. The width of the block does not change that count.
How many concrete blocks per square foot?
1.125, for any standard block, because they are all 8 by 16 nominal on the face. Inverted, one block covers 0.888 square feet. A 4 inch block and a 12 inch block cover the same wall area and differ only in mortar, grout and weight.
How many blocks does a bag of mortar lay?
About 13 standard 8 inch blocks per 80 pound bag, face shell bedded. A 40 by 8 foot wall at 360 block takes 28 bags. Twelve inch block drops it to about 11 a bag, so the same wall takes 34.
How much grout do I need to fill block cells?
About 0.19 cubic feet per foot of height for each grouted cell in 8 inch block. Cells at 48 inches on a 40 by 8 foot wall is 11 cells and 16.5 cubic feet. Fully grouted, the same wall size in 8 inch block runs near 0.28 cubic feet per square foot of wall.
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Common sizes, worked out
The same calculator with the numbers already filled in, one page per size, each ending in its own material list.