The coursing dimension is the unit plus one joint
Nothing in masonry is laid at its own size. A modular brick specifies at 2-1/4 inches high, but it occupies 2-1/4 plus a bed joint, and that sum is the only number that matters once you are stacking. At a strict 3/8 joint the course height is 2-5/8, which gives 4.571 courses per foot. At the 7/16 joint that modular coursing assumes, it is 2-2/3, which gives exactly 4.5 courses per foot and lands three courses on 8 inches. Both are correct. They are answers to different questions.
Block behaves the same way. An 8x8x16 block is 7-5/8 high and specifies to an 8 inch course, so a wall is a whole number of 8 inch steps and every dimension on the drawing wants to be a multiple of 8. When it is not, somebody has to decide where the difference goes, and that decision is better made on paper than by the bricklayer at four in the afternoon.
| Unit | Unit height | Course at 3/8 | Courses per foot | Height of 10 courses |
|---|---|---|---|---|
| Modular brick | 2-1/4 | 2-5/8 | 4.571 | 2 ft 2-1/4 in |
| Queen brick | 2-3/4 | 3-1/8 | 3.840 | 2 ft 7-1/4 in |
| King brick | 2-5/8 | 3 | 4.000 | 2 ft 6 in |
| Utility brick | 3-5/8 | 4 | 3.000 | 3 ft 4 in |
| CMU 8 in high | 7-5/8 | 8 | 1.500 | 6 ft 8 in |
| CMU half-high | 3-5/8 | 4 | 3.000 | 3 ft 4 in |
Where the difference goes
Say the height to reach is 48 inches and the unit is modular brick. Eighteen courses at a 3/8 joint is 47-1/4, three quarters of an inch short. There are three ways to spend that three quarters.
Spread it across the eighteen bed joints and each one grows by one twenty-fourth of an inch, which is 0.042, taking the joint to 0.417. Nobody on earth can see that, and it happens to be exactly the modular coursing joint. Spread it across two joints and each grows by 3/8, doubling them, which everybody sees. Put it all in one joint and you have a 1-1/8 inch bed line that looks like a repair. Cut a course to make it up and you get a sliver of brick under the sill.
The lesson is that the adjustment is free when it is divided by a large number and ugly when it is divided by a small one. That is why the decision has to be made at the bottom of the wall. Once you are three courses from the sill, there are only three joints left to spread it over.
The horizontal layout has the same problem and worse consequences
Vertically you can lose a sixteenth per joint and nobody notices. Horizontally the head joints are visible in a vertical line every other course, and a wall where the last unit in each course is a two inch bat reads as a mistake from the road. Twelve feet of wall is 144 inches, which is exactly 18 modular brick modules at 8 inches, which is why 8 inch modules and 4 foot dimensions get on so well.
When the length is not a multiple of the module, the choices are to adjust the head joints across the run, to work from both ends toward a deliberate cut in the middle where a downpipe or a shadow will hide it, or to move the opening. The one thing not to do is start at one end at a perfect 3/8 and discover the problem at the other. Dry-lay a course on the footing before you mix anything. It costs twenty minutes and it is the only way to see the layout with your eyes rather than your arithmetic.
What this page assumes and where it will be wrong
It assumes a running or stack bond where every course is the same height, a single unit type, and units that match their specified dimensions. It does not know about a thickened first bed joint used to level a footing that is out, which is the usual place a wall recovers from a bad slab. It does not know about soldier courses, rowlock sills or a bond beam course of a different height, all of which break the constant course height this arithmetic depends on. Where a wall has those, course it in segments between them.
Once the layout is settled, the brick and block calculator turns it into a unit count and mortar, the block wall calculator adds grout and bond beams, and the mortar mix calculator handles the proportions. Whether a given wall height, thickness or reinforcement is acceptable is a structural and code question that belongs with the building department and, above anything modest, with an engineer.
Questions people ask
How many brick courses are in a foot?
For modular brick, 4.571 courses at a strict 3/8 inch bed joint, or exactly 4.5 at the 7/16 joint that modular coursing assumes so that three courses land on 8 inches. King brick gives exactly 4 per foot at 3/8 because it courses at 3 inches. Utility brick gives 3. Standard 8 inch block gives 1.5. The figure you want is 12 divided by the course height, and the course height is always the unit plus one joint.
What is the largest mortar joint I can run?
That is a specification and a workmanship question rather than an arithmetic one. As a practical matter, joints much beyond about a half inch get hard to keep straight, hold more water at the face, and start to look like a repair. Joints under about a quarter inch leave nothing for the unit tolerance to hide in, so every long or short brick in the pallet shows. The fields here let you set your own limits because the answer depends on the unit, the specification and what the wall has to look like.
My wall height falls between two courses. What do I do?
Divide the shortfall by the number of bed joints below it and add that much to each joint. If the result stays inside a joint range you are willing to run, the wall lands on the dimension and nobody can tell. If it does not, the realistic options are to move the dimension, change to a unit with a different height, or absorb the difference in the slab or footing before the first course goes down. Cutting a course near the top is a last resort because it is permanently visible.
Should I measure course height from the footing or from grade?
From whatever the first course actually sits on, because that is where the stack starts. If the wall has buried courses below finished grade, they count in the coursing even though nobody sees them. This is also the place where a footing that is out of level gets corrected, by varying the first bed joint across the run, and that variation has to come out of the coursing arithmetic rather than being added on top of it.
Does the unit tolerance really matter over a wall?
It compounds, which is what makes it matter. A sixteenth of an inch of extra height per unit across twenty courses is an inch and a quarter of drift, which is enough to lose a window head. Measure ten units stacked on edge and divide by ten to get the real average height, and use that instead of the catalogue figure. Masons who work to a story pole are checking exactly this every few courses.