Where bricks per square foot comes from
A brick is sold by its actual size but laid on a module that includes the joint. A modular brick specifies at 7-5/8 long by 2-1/4 high. Add a 3/8 inch joint on the end and on the bed and it occupies 8 by 2-5/8 inches of wall face, which is 21 square inches. Divide 144 by 21 and you get 6.86 bricks per square foot.
The figure the trade quotes is 6.75, not 6.86. That comes from modular coursing, where three courses are meant to land on exactly 8 inches. Three bricks at 2-1/4 is 6-3/4, leaving 1-1/4 inches split across three bed joints, or about 7/16 each rather than 3/8. The module becomes 8 by 2-2/3, which is 21.33 square inches, and 144 divided by that is 6.75. Both numbers are correct for the joint they assume. The calculator uses whatever joint you type, so if you want the 6.75 answer, enter 0.4167.
| Unit | Actual size | Face module at 3/8 | Per sq ft |
|---|---|---|---|
| Modular brick | 7-5/8 x 2-1/4 | 8 x 2-5/8 | 6.86 |
| Queen brick | 7-5/8 x 2-3/4 | 8 x 3-1/8 | 5.76 |
| King brick | 9-5/8 x 2-5/8 | 10 x 3 | 4.80 |
| Utility brick | 11-5/8 x 3-5/8 | 12 x 4 | 3.00 |
| CMU 8x8x16 | 15-5/8 x 7-5/8 | 16 x 8 | 1.125 |
Every block in the 8 inch high, 16 inch long family gives 1.125 units per square foot regardless of how thick it is, because the face is the same. Thickness changes the mortar and the weight, not the count.
Mortar, and why the bag will disagree with you
The mortar in a wall is the difference between the module and the unit, multiplied by how deep the bedding runs. For a modular brick that face difference is 21 minus 17.16, which is 3.84 square inches, and a full bed 3-5/8 deep makes 13.9 cubic inches per brick. A thousand bricks is 13,900 cubic inches, or about 8 cubic feet before waste.
Block is different because it is bedded on the face shells rather than across the whole unit. Two shells at roughly 1-1/4 inches each is 2-1/2 inches of bedding instead of 7-5/8, so a standard block takes about 22 cubic inches, and a hundred blocks about 1.3 cubic feet net.
Now the honest part. Bag manufacturers quote coverage well below what this geometry gives, sometimes half. They are not wrong so much as pessimistic: their figure assumes generous buttering, mortar that stiffens on the board, and the amount a first-timer drops on the scaffold. If you have laid masonry before, the geometric figure plus 20 to 25 percent is close. If you have not, budget toward double and take the unopened bags back.
Openings, wythes and the parts this does not count
Deduct openings at their rough size. Do not try to add back for the jambs, because the cut units around an opening are exactly where your waste percentage gets spent. A brick veneer is one wythe. A solid wall two bricks thick is two, and the calculator doubles both the count and the mortar, but it does not add the collar joint between the wythes. On a filled collar joint add roughly the wall area times the collar width, which for a 3/4 inch collar on 100 square feet is about 6 cubic feet of extra mortar.
Not counted here: grout in reinforced block cells, which is a much larger volume than the mortar and is usually ordered as ready-mix; wall ties; lintels; flashing; weeps; and the footing. On a block wall the grout can easily exceed the mortar by a factor of five.
Two things will move your real number more than anything on this page: the actual dimensions of the pallet that shows up, and how consistently the mason runs the joint. Pull five units off the pallet, measure them, and if they are not what the spec sheet says, change the numbers here before you place the order rather than after.
Questions people ask
How many bricks are in a square foot?
For modular brick, between 6.75 and 6.9 depending on the joint. Strict 3/8 inch joints give 6.86; the modular coursing convention where three courses make 8 inches gives 6.75. Queen brick is about 5.76 per square foot, king about 4.8, and utility about 3. Standard 8x8x16 block is 1.125 per square foot. All of these assume the actual specified sizes and a 3/8 joint, and all of them shift if your supplier ships units at a different tolerance.
How many blocks do I need for a 100 square foot wall?
About 113 standard 8x8x16 blocks before waste, since block runs 1.125 units per square foot. Add 5 percent for cuts and breakage and order 119. That count is the same for 4, 6, 8 and 12 inch block because the face dimension does not change. What changes is the weight to lift, the mortar depth, and whether you can lay it single-handed.
How much mortar per 1000 bricks?
About 8 cubic feet net for modular brick with 3/8 joints and full bedding, which is the joint geometry with nothing added. With a working waste allowance of 25 percent, call it 10 cubic feet, or 16 bags of 80 lb premix at the 0.66 cubic foot yield most of them quote. Bag labels typically imply closer to 30 bags per thousand. The gap is waste assumptions, not arithmetic. Buy in the lower half of that range if you are experienced and the upper half if you are not.
How much sand do I need if I mix my own mortar?
Roughly one cubic foot of damp loose sand per cubic foot of finished mortar. That sounds wrong until you realise the cement and lime paste mostly fills the voids between sand grains rather than adding volume. Damp masonry sand runs somewhere near 100 lb per cubic foot, with a genuine range of about 90 to 110 depending on moisture, so a cubic yard weighs a little over 1.3 tons. Sand is cheap by the yard and expensive by the bag, so if the job needs more than about 15 cubic feet, order bulk.
Does the joint thickness really change the count that much?
Yes, more than people expect on small units. Going from a 3/8 to a 1/2 inch joint on modular brick changes the module from 8 x 2-5/8 to 8-1/8 x 2-3/4, and the count from 6.86 to 6.44 per square foot. Over a 120 square foot wall that is about 50 bricks. It also increases the mortar by roughly a third. On block the effect is much smaller because the unit is large relative to the joint.