Why the corners are the whole problem
A wall is measured by its face and the arithmetic is honest: area divided by module. A closed stack is not, because the four corners belong to two faces at once. Measure the outside of a 24 inch square chimney and you get 96 inches of perimeter. But the brick at each corner turns, and the length of masonry that actually gets laid is the perimeter of the centreline of the wythe, which is 96 minus four times the wythe thickness.
For modular brick that thickness is 3-5/8, so the centreline perimeter is 96 minus 14-1/2, which is 81-1/2 inches. At an 8 inch module that is 10.19 bricks per course against the 12 you get from the outside face. Over the 28 courses in a six foot stack the difference is 51 bricks, and over a two storey chimney it is well past two hundred. It is the same centreline rule that catches people measuring a footing around a building perimeter.
| Outside plan | Outside perimeter | Centreline perimeter | Modular brick per course |
|---|---|---|---|
| 16 x 16 | 64 in | 49.5 in | 6.19 |
| 20 x 20 | 80 in | 65.5 in | 8.19 |
| 24 x 24 | 96 in | 81.5 in | 10.19 |
| 24 x 36 | 120 in | 105.5 in | 13.19 |
| 32 x 48 | 160 in | 145.5 in | 18.19 |
Solid columns are counted in plan, not in perimeter
Two wythes of modular brick already use 7-1/4 inches of the plan, so anything at or under that size has no core at all and the calculator counts it solid. Well above that threshold the core is often filled anyway, because a 10 inch square pillar with a 3 inch hole up the middle is more trouble to build hollow than to build solid. A solid column is counted by how many bricks fit in the plan: the plan area divided by the area one brick occupies lying flat, which is its module length by its bed depth plus a joint. For modular brick that is 8 by 4 inches, or 32 square inches per brick, so a 16 inch square column takes 256 divided by 32, which is 8 bricks a course.
Real solid columns are laid in a bond that rotates each course so the joints break, and the practical count comes out slightly above the geometric one because the bond needs closers and bats. That is what the waste percentage on this page is for, and it is why the default is higher than the 5 percent a plain wall gets.
What a counting page will not tell you about a chimney
This calculator counts brick, mortar, flue sections and a cap. That is the easy part of a chimney and the least consequential. What size flue a stove or fireplace needs, how high the stack has to rise relative to the roof and to anything nearby, what clearance the masonry needs to framing and roof sheathing, whether the liner has to be continuous, and how the flashing and counterflashing are built are all determined by the adopted code, the appliance manufacturer and the inspector who signs it off. They vary by jurisdiction and they change.
An existing chimney adds another layer. Anything built before roughly 1980 can carry lead paint on rendered or painted masonry, and older buildings can carry asbestos in flue components and surrounding materials. Disturbing either is a specialist job with its own rules. Name it, test it, and hand it to somebody licensed for it rather than taking an angle grinder to it on a Saturday.
What to buy alongside the count
Footings, ties, reinforcement, flashing and the wash on the cap are all outside this page. For the footing under the stack the concrete footing calculator handles volume and bar, and the mortar mix calculator covers the proportions if you are mixing rather than buying bags. For the walls the column ties into, the brick and block calculator works from face area. For the weight of what you have just ordered and how many trips it takes, the masonry weight and pallet calculator is on this site.
Questions people ask
How many bricks are in a chimney?
Work it from the centreline perimeter, not the outside. A 24 inch square stack in modular brick is 81-1/2 inches of centreline per course, which is 10.19 bricks. A six foot stack is 28 courses, so about 285 bricks before waste and 309 ordered with 8 percent added. Double the height and you double the count. The single most common error is using the outside perimeter, which on that stack adds nearly two bricks a course.
What is the difference between a hollow and a solid column?
A hollow column is one wythe of masonry wrapped around an open core, which is what a chimney is and what most gate pillars and mailbox posts are. A solid column has brick filling the whole plan. Two wythes of modular brick at 3-5/8 each use 7-1/4 inches of the plan, so a stack at or below that size cannot have a core and the calculator switches to a solid count automatically. In practice small pillars get built solid well before that limit, because a narrow core is more awkward to lay around than to fill.
How much mortar does a brick column take?
The same per brick as a wall does, because the joint geometry is identical: about 13.9 cubic inches for modular brick fully bedded with 3/8 joints, which is roughly 8 cubic feet per thousand bricks before waste. A 24 inch square six foot stack of about 285 bricks needs around 2.3 cubic feet net, or near 2.9 with a quarter added for droppings and board leftovers, which is five 80 lb bags.
Do I need a footing under a brick pillar?
Masonry is heavy and it does not tolerate differential movement, so what it bears on matters more than for most things you can build. What size and depth of footing a particular column needs depends on the load, the soil, the frost depth adopted where you are and whether it is attached to anything else. That is a question for the building department, and for anything tall or load-carrying, an engineer. This page counts the brick above it and nothing below it.
Can I use this for a mailbox or gate pillar?
Yes, and that is one of the better uses for it. Those are usually hollow stacks in the 16 to 24 inch range, two to five feet tall, and the count comes out in the low hundreds of brick. Set the height to the masonry only, not to the top of whatever sits on it, and remember that the cap and the footing are separate purchases. Pillars near a driveway or road may also have local rules about what can be built in a right of way.