Brick calculator

6.75 per square foot is one brick size out of ten

The figure everyone quotes is real, and it is narrow. Brick Industry Association Technical Note 10, Table 4, gives 675 modular brick per 100 square feet of wall at a 3/8 in joint. Modular brick is nominal 4 × 2-2/3 × 8 in, specified 3-5/8 × 2-1/4 × 7-5/8 in.

Change the format and the number moves a long way:

That is a 2.25 : 1 spread between modular and utility. Order a King-brick veneer off the 6.75 figure and you buy 48% more brick than the wall can hold. This is also why BIA tells you to specify brick by its dimensions rather than its name: the same word means different sizes at different plants.

Why the table says 6.75 and the arithmetic says 6.86

Worth knowing, because it is the one place brick estimating is genuinely slippery. Take the specified modular brick and add a true 3/8 in joint to both dimensions: 7-5/8 + 3/8 = 8 in long, 2-1/4 + 3/8 = 2-5/8 in high. Then 144 ÷ (8 × 2.625) = 6.86 per sq ft, not 6.75.

Both are right. Modular brick is dimensioned so that three courses come to exactly 8 in, and three 2-1/4 in brick are only 6-3/4 in, so the bed joint has to be about 0.42 in — a shade over 3/8. BIA's modular table is computed from the nominal 2-2/3 in course, which is why it lands on 6.75. Its non-modular table is computed from specified dimensions plus the joint, which is exactly what this calculator does — and it reproduces those rows to the digit. Standard brick at 8 in long on a 2.625 in course gives 6.55; Queen and King at their upper specified lengths give 5.50 and 4.55. Same numbers as the book.

That is why the input above asks for the height of one course rather than a bed joint. It is what a mason marks on a course rod, and it removes the ambiguity: 2.67 for modular, 2.625 for Standard, 3.125 for Queen and King.

A fatter joint changes the mortar, not the brick count

This surprises people, and BIA's table is unambiguous about it. Table 4 gives one brick-per-100-sq-ft figure covering both joint widths, and two mortar volumes. Modular is 675 brick at 3/8 in and 675 at 1/2 in — but 5.5 cu ft of mortar at 3/8 in and 6.9 at 1/2, which is 25% more.

The reason is that the brick is dimensioned around the joint, not in spite of it. Modular brick is specified at 7-5/8 in so that the unit plus a 3/8 in joint is an 8 in module; lay it to 1/2 in joints and the wall simply courses out on a slightly longer module, so the count per square foot barely moves while the volume of the joints themselves goes up by a quarter.

Practically: if you are laying reclaimed or hand-made brick to a 1/2 in joint, your brick order is fine off either column — your mortar order is not.

"37 bricks per bag" cannot be applied to your brick

The QUIKRETE Mortar Mix and Mason Mix data sheets state that an 80 lb bag "will lay up to 37 standard bricks or 13 standard 8 × 8 × 16 blocks". That figure is true and it is the wrong tool, because standard is one row out of twenty-four.

Here is the proof, and it is decisive. Meridian, 6-in Through-Wall Meridian and 8-in Through-Wall Meridian all present a 4 × 16 in nominal face. All three give 225 brick per 100 sq ft. Every dimension you can measure on the face is identical. Yet BIA Table 4 puts their mortar at 3.5, 5.4 and 7.3 cu ft per 100 sq ft — the widest is 2.09 times the narrowest, because the units are 4, 6 and 8 in through the wall. One set of face dimensions, three correct answers. No formula over the numbers this page collects can return them, so it does not try: mortar comes from the table.

Bags then come from a volume, not a count. Crossing QUIKRETE's 37 standard bricks with BIA's 14.5 cu ft per 1000 standard brick gives 0.5365 cu ft placed per 80 lb bag, and every profile divides by that. The difference is not academic: 100 sq ft of queen is 6.7 cu ft, so 13 bags — counting 550 ÷ 37 says 15. Bigger units mean fewer, larger joints and less mortar per square foot.

And note the second bag entirely. Masonry cement (QUIKRETE No. 1125-70) is binder only; one 70 lb bag plus 240 lb of sand lays about 144 standard bricks. That is why published mortar quantities for one job differ by nearly four times. The mortar calculator does both and shows the sand.

Why courses × bricks-per-course gives a bigger number

Check this page by hand and you will get two different answers, so here is the difference before it costs you.

Count a 10 × 8 ft wall in modular brick the obvious way: a 10 ft course takes 16 bricks — ceil((120 + 3/8) ÷ 8), because 15 of them span only 119-5/8 in and the last one is a cut. There are 36 courses. That is 576 brick.

The area coefficient says 540 — 80 sq ft × 6.75. Thirty-six fewer, one per course, and it is the 540 that this page buys from.

The offcut is why. Running bond starts alternate courses on a half brick, so the piece you cut off the end of one course is exactly the piece the next course needs at its other end. The cut brick is not waste; the bond consumes it. Rounding each course up and then multiplying by the number of courses assumes you throw every offcut away, which is neither what a bricklayer does nor what BIA's published coefficient measures.

So the two outputs answer two questions and both are right. Bricks per course is a fitting question — how many pieces sit in one lift, last one cut — and it rounds up. Bricks to buy is a quantity question, and it comes from the published area figure. The one place they agree is a single course with nothing above it to pass the offcut to: there, the fitting answer is the buying answer.

What the mortar figure assumes

BIA Table 4 is not universal and says so. The numbers above hold for:

• Running or stack bond. A bond with headers needs more of both. BIA's own correction for common bond with full headers every fifth course is +1/5 on the brick and +1/15 on the mortar; Flemish bond is +1/3 on the brick and +1/9 on the mortar.
• Fully bedded units. Hollow brick laid face-shell only take less, by roughly the void fraction — commonly 25 to 35%.
• Theoretical joint volume, waste excluded. BIA states this outright, which is why mortar has its own waste field here rather than borrowing the brick one. 15 to 25% is the usual allowance.

If your job is outside that, the volume is still the right starting point — apply the correction and buy to the corrected figure.

Note that the mortar here is worked from wall area, not from a brick count, which is why your brick breakage allowance never reaches it. A brick that arrives cracked or gets cut in half does not add joint to the wall, so mortar carries its own allowance and nothing else.

Two things that quietly add brick

• Wythes. A veneer is one wythe. A solid two-wythe wall is double the brick, and if the collar joint between the leaves is mortared solid, BIA Table 5 puts that at 3.13 cu ft of mortar per 100 sq ft at a 3/8 in joint.
• Bond pattern. Everything above assumes running bond. Per BIA Table 6, Flemish bond adds 1/3 to the brick count and 1/9 to the mortar; common bond with full headers every sixth course adds 1/6 to the brick and 1/18 to the mortar. On 1,000 brick the Flemish correction is 333 units — not a rounding matter.

What this will not tell you

Whether the wall needs a lintel, how it is tied back, or how it is flashed and weeped. A brick veneer is a rain screen and it fails at the details, not at the brick count. Those belong to your local code and, for anything structural, to an engineer.

When these numbers stop describing your job

Everything above is the field of a flat rectangular wall in clay brick. Five places where your wall is not that:

• Openings are entered as an area, not a position. They come out of the count at the same density as the rest of the wall. A real opening does the opposite of that at its edges: cut brick down both jambs, a soldier course or a lintel over the head, a rowlock sill under it. Those are extra units at a different density, and none of them are here.
• Nothing is counted for the details. Corner returns, a soldier or header course as a band, a rowlock cap on a garden wall, an arch, a chimney corbel — all of it is brick you buy and none of it is in the coefficient.
• A wall that is not a rectangle has to be split. A gable, a curved wall, a stepped garden wall down a slope: enter each rectangle separately and add them. Curves also consume brick faster than their developed area suggests, because the joints open on one face.
• Choose a custom size and the mortar goes blank on purpose. It is not a failure — the three Meridian rows above show that face dimensions cannot produce a mortar volume. If you substitute the nearest tabulated profile to get a number back, you have changed the brick count too, so check it against your supplier's own figure.
• Two joint widths exist in this table and no others. BIA publishes mortar at 3/8 in and 1/2 in only. Wider joints on reclaimed or hand-made brick are outside it, and the volume will be low.