Why brick count uses nominal size, not the brick in your hand
Why is the square-foot count
A modular brick is sold as 3-5/8 × 2-1/4 × 7-5/8. Laid with a 3/8 joint it occupies 4 × 2-2/3 × 8 — the nominal size. Units per square foot are in inches. For a standard modular that is . If you divide wall area by the actual 7-5/8 × 2-1/4 face, you under-count, then someone subtracts the joint a second time and the pallet count falls apart.
Openings are deducted once, as square feet of wall you will not lay. Doors, windows, and a fireplace breast come off the gross L × H before you multiply by 6.75. A double-wythe wall is two faces. This calculator is one wythe. Running it once and calling it a cavity wall leaves the backup wythe unordered.
Mortar bags on this page are a Type N 80 lb estimate for 3/8 joints. They are not a mix design. Sand tonnage follows that same joint, not a lab sieve. Type S for a below-grade foundation wall is a different bag count and a different spec — do not keep the Type N number after the engineer changes the mortar.
Worked field example
36-foot wall, 8 feet high, modular brick, two 3 × 5 windows (30 sf). Not the 30 × 8 / 40 sf default.
Gross is 36 × 8 = 288 square feet. Minus 30 is 258. At 6.75 modular bricks per foot that is 1,742 net units. Ten percent breakage and cuts is about 1,916 to order. Course count is 8 × 12 ÷ 2.667 ≈ 36 courses — check that the last course dies under the plate or the lintel, not mid-brick.
If those windows are in a double-wythe veneer-plus-backup, this number is the veneer only. The backup CMU is a second takeoff on the 8x8x16 unit, not “add 10 percent” to the brick count.
What IRC R606, TMS, and ASTM actually govern
R606 is empirical masonry in the IRC. TMS 402/602 is the standard most engineered walls point to. ASTM C216 is face brick; C90 is loadbearing CMU. None of them change the 144 ÷ (L × H) takeoff. They change whether the wall is allowed, how it is tied, and what unit you may put in the wall.
Product and wall rules — count is still nominal
- Provision
- IRC R606
- Limit
- Empirical masonry: height, thickness, and lateral support
- Failure mode
- An 8-foot veneer taken off as if it were a 16-foot unreinforced wall
- Provision
- TMS 402/602
- Limit
- Engineered masonry, ties, grout, inspection
- Failure mode
- Using this brick count as a structural design
- Provision
- ASTM C216 / C90
- Limit
- Facing brick grade; loadbearing CMU
- Failure mode
- Ordering C62 interior brick on a weather face
| Provision | Limit | Failure mode |
|---|---|---|
| IRC R606 | Empirical masonry: height, thickness, and lateral support | An 8-foot veneer taken off as if it were a 16-foot unreinforced wall |
| TMS 402/602 | Engineered masonry, ties, grout, inspection | Using this brick count as a structural design |
| ASTM C216 / C90 | Facing brick grade; loadbearing CMU | Ordering C62 interior brick on a weather face |
Where the field usually goes wrong
Dividing by the actual brick and then subtracting 3/8 again is the classic double deduction. Nominal already includes the joint. The next miss is a double wythe: veneer plus backup is two unit counts, two mortar tickets, and usually two specs (C216 and C90). Soldier courses and rowlock sills eat extras that a flat sf takeoff does not see — raise waste or add a line, do not invent a new units-per-foot.
Openings with steel lintels still need brick above the head. Deduct the glazed hole, not a full-height strip to the plate. CMU is 1.125 blocks per sf for 8x8x16 nominal (144 ÷ 16 ÷ 8). Treating a 6-inch block as an 8-inch face count will short the wall in length, not in height. Grout in cells is a concrete takeoff, not more Type N mortar. Mortar is the joint; grout is the core.
Frequently asked questions
Why use nominal size instead of the brick I can measure?
The joint is in the module. A 7-5/8 brick plus 3/8 is 8 inches. 144 ÷ (8 × 2.667) = 6.75. Measuring the clay only under-counts.
Do I deduct openings?
Yes, once, as square feet. Lintels still need brick above the head.
How do I take off a double-wythe or cavity wall?
Run twice — once per wythe. Veneer plus CMU backup is two products.
Is 6.75 bricks per square foot always right?
For modular brick with a 3/8 joint, yes. Queen and king units differ. Pick the unit on the form.
Does this include mortar and sand?
Type N 80 lb bags and sand for 3/8 joints. Not a mix design, and not grout in CMU cells.
What about soldier courses and arches?
They eat extras. Add a line or raise waste. Do not change the 6.75 field factor.
Is this a structural masonry design?
No. R606 and TMS decide if the wall stands. This page counts units.