How the brick math works
Masons estimate brick the way the Brick Industry Association recommends in its Technical Note 10: the wall-area method. Work out the wall's net area (length times height, less the doors and windows), then multiply by the number of bricks it takes to cover a square foot in your brick size and joint. BIA publishes that number for every standard size, along with the mortar the joints hold. Add at least 5 percent for chipped bricks and cuts, round up, and you have your order.
Mortar is the one place we leave BIA's table for the bag. BIA counts the mortar that ends up inside the joints; the bag makers count how many bricks one bag actually lays, which is the number you shop by. Both are on the page, so you can see the difference, and it is bigger than you might guess.
The formula
bricks per sq ft (modular) = 144 ÷ [(brick length + joint) × (brick height + joint)] · mortar bags = bricks in the wall ÷ bricks per bag, rounded up
Lengths and heights are in feet, openings in square feet, and waste is a percentage (5 percent is BIA's minimum). For modular brick the length and height with the joint are the nominal size, so a modular brick with its 3/8 in joint fills exactly 8 by 2-2/3 inches of wall. Bricks per bag comes from the mortar makers: 35 modular bricks per 80 lb bag at a 3/8 in joint.
Worked example
A 24 ft by 8 ft wall with a 3 by 7 ft door (21 sq ft) and a 3 by 4 ft window (12 sq ft), in modular brick with 3/8 in joints. The wall is 192 sq ft, less 33 sq ft of openings, so 159 sq ft of brick. At 6.75 bricks a square foot that is 1,073.25 bricks in the wall; add BIA's 5 percent and it comes to 1,126.91, so buy 1,127 bricks. At 35 bricks an 80 lb bag, the mortar is 1,073.25 ÷ 35 = 30.66, so buy 31 bags. The wall is 36 courses tall, exactly, because three modular courses rise 8 inches.
Headline: 1,127 modular bricks and 31 bags of mortar for 159 sq ft of wall.
Same wall, different brick: the size changes everything
The brick you pick moves the count more than anything else you enter. That same 159 sq ft wall takes 1,127 modular bricks, 1,094 standard, 919 queen, 760 king, 752 Norman, and just 501 utility bricks. The reason is plain geometry. A utility brick is one and a half times as long as a modular brick and one and a half times as tall, so its face covers 2.25 times the wall, and the count drops to 44 percent. A Norman brick is the modular brick stretched to 12 inches: same height, half again as long, and exactly two thirds of the bricks.
That geometry is also why modular counts are so tidy. A modular brick plus its joint is sized to a 4 inch grid, so its face with the joint is exactly 8 by 2-2/3 inches, and 144 square inches divided by that is 6.75 bricks a square foot, precisely the 675 per 100 square feet in BIA's table. Fewer bricks is not automatically cheaper, though: a bigger brick costs more each, and each one takes more mortar, as the bag column in the table under your result shows.
How much mortar you need, two ways
BIA's table says the joints of 1,000 modular bricks hold 8.1 cubic feet of mortar at a 3/8 in joint. The bag makers see it from the other side: Quikrete rates an 80 lb bag of its mortar mix at up to 37 standard bricks, Sakrete at 35, and TCC Materials at 35 to 40 modular bricks, 33 queen, 30 king, or 25 utility. Those counts are what we use, taking 35 for everyday brick.
Put the two side by side and the bags come out generous. On the worked example the joints hold 8.75 cubic feet, while the 31 bags make about 22.32 cubic feet at TCC's 0.72 cubic feet a bag, 2.55 times as much. That is not an error on either side. BIA is measuring the finished wall; the bag counts describe real bricklaying, where mortar is furrowed, buttered, struck off, dropped, and left to stiffen on the board. BIA itself adds 15 to 25 percent to its net mortar, and notes that the masons' old rule of eight bags of masonry cement per 1,000 modular brick carries an unspecified amount of waste. Buy by the bag count, and let BIA's figure be the floor.
Does a thicker mortar joint change the count?
For modular brick, no, and it is a clever bit of standardization. Modular brick are made in two lengths, 7-5/8 in for a 3/8 in joint and 7-1/2 in for a 1/2 in joint, so the brick plus its joint always fills the same 8 inch module. The count stays at 6.75 a square foot; only the mortar changes, from 5.5 to 6.9 cubic feet per 100 square feet, about 25 percent more. Non-modular brick keep their size, so a thicker joint really does mean fewer of them: a standard brick drops from 655 per 100 square feet at a 3/8 in joint to about 618 at 1/2 in, the figure BIA's own mortar columns imply.
Before you lay the first course
A brick wall is only as good as what it stands on and what holds it. Brick veneer on a house needs a footing or ledge to sit on, metal ties into the framing behind it, and flashing and weep holes at the bottom so water that gets behind the brick can get back out. A freestanding garden wall has no house to lean on, so its footing, thickness, and height are an engineering and code question well before they are a brick-count question; your building department is the first call. For the footing itself, our concrete calculator does the volume, and our square footage calculator helps with walls that are not simple rectangles.