Brick Calculator
Derived from your brick size, not the seven-per-foot rule.
Work out Brick. Derived from your brick size, not the seven-per-foot rule. Counts the extra post, the leftover box and the gap between boards.
US modular is 7⅝ × 2¼.
From your mortar product. Leave at zero to skip.
Bricks needed
720
6.86 per square foot
The trade rule of seven bricks per square foot is right for exactly one brick: US modular with a ⅜ inch joint gives 6.86. It comes from the unit cell — the brick plus its joint on two sides — and any other size or joint moves it, which is why both are inputs here.
How the Brick Calculator works
The trade rule is seven bricks to the square foot, and it is right for exactly one brick size. A brick occupies its own face plus a mortar joint on two sides, so US modular at 7⅝ by 2¼ with a ⅜ joint works out at 6.86 per square foot — which is where the rule comes from. Change the brick or the joint and the number moves, which is why both are inputs here rather than a constant.
Also known as: how many bricks do I need · brick wall calculator · bricks per square foot · brick and mortar calculator
Where seven per square foot comes from
A brick occupies its own face plus a mortar joint on two sides. So the unit cell is (length + joint) by (height + joint), and the count per square foot is 144 divided by that area in square inches.
US modular brick is 7⅝ by 2¼ with a ⅜ joint, giving a cell of 8 by 2⅝ — 21 square inches. 144 ÷ 21 = 6.857.
That is the whole derivation of the trade rule, and it shows immediately why the rule only holds for that one brick.
In practice
A hundred square feet of modular brick is 686 bricks before waste, or 720 with five percent.
Change the joint from ⅜ to ½ and the cell becomes 8⅛ by 2¾ — 22.34 square inches, so 6.44 per square foot. The same wall now needs 644 rather than 686, a six percent difference from an eighth of an inch of mortar.
Queen, king and utility bricks all differ again, which is why entering the actual dimensions beats applying the rule.
Where the figure deceives
It assumes a single wythe of stretcher bond. Any pattern with headers, a double-wythe wall, or a bond that turns bricks through ninety degrees changes the count materially.
Waste on brick is not just cuts. Bricks arrive chipped and broken, and colour variation means some get rejected on sight, so ordering to the exact number reliably leaves you short.
The mortar estimate is rougher than the brick count. Joint size, wall thickness and how much is wasted on the board all move it, and product yields differ enough between mixes that the bag figure is a starting point rather than an order.
Acting on it
Measure a sample brick rather than trusting a nominal size, and check the joint the mason intends to use.
Order from one batch where colour matters. Brick shading varies between production runs in a way that shows on a finished wall.
Add for breakage on top of cutting waste — they are separate losses.
Frequently asked questions
How many bricks do I need?
Divide 144 by the brick's face area including its mortar joint, which gives bricks per square foot, then multiply by the wall area and add waste. Standard US modular comes out at 6.86 per square foot.
Where does 'seven bricks per square foot' come from?
From modular brick with a ⅜ inch joint — the unit cell is 8 by 2⅝ inches, or 21 square inches, and 144 divided by 21 is 6.86. It is a rounded result for one specific size, not a general rule.
Does the mortar joint change the count?
Yes, and more than people expect. Going from a ⅜ to a ½ inch joint drops the count by around five percent, because each brick is effectively larger.
How much waste should I allow?
Around five percent for a straightforward wall, more where there are many cuts around openings. Bricks also arrive with breakages, so ordering to the exact count is asking for a short delivery.
How much mortar will I need?
It depends on joint size and wall thickness. This estimates the mortar volume from the joint fraction of the wall, and converts to bags at whatever yield your product states — those vary considerably between mixes.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
<iframe src="https://www.thecalclibrary.com/embed/brick-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Brick Calculator"></iframe>The only condition is that the credit line stays visible. It sits inside the frame, so you do not have to do anything to keep it.
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