How this instrument works
Mortar mix is sold in standard bags, most commonly 80lb, and each bag lays a certain number of bricks or blocks depending on joint size and unit dimensions. This calculator divides your total brick or block count by a units-per-bag coverage figure and rounds up, since a partial bag still means buying a whole one.
That coverage figure is a typical rate, not a fixed universal constant. A standard 80lb bag commonly lays around 36 standard bricks at typical 3/8-inch joints, or around 12 standard 8×8×16-inch CMU blocks — but real coverage spreads meaningfully around those numbers depending on the brand of mortar mix, joint width, and the exact size of your specific brick or block, with some sources citing ranges as wide as 36-65 bricks per bag or 12-15 blocks per bag. Check your specific mortar product's packaging or a manufacturer's coverage chart for the most accurate figure on a large job.
The two preset options here, standard brick and 8×8×16 CMU block, cover the most common cases, but if your project uses a nonstandard unit size or a specialty mortar, look up that product's actual stated coverage and use it in place of the default.
- Select Unit type — standard brick or 8×8×16in CMU block, each with a typical per-bag coverage rate.
- Enter Number of bricks / blocks — your project's total unit count.
- Read 80lb mortar mix bags needed — rounded up to the next whole bag, since partial bags aren't sold.
Worked example — 500 standard bricks
Select Standard brick (≈36 per 80lb bag) and set Number of bricks to 500. Bags needed = ceil(500 ÷ 36) = ceil(13.889) = 14 bags.
Switch to 8×8×16in CMU block (≈12 per 80lb bag) for a 200-block wall project: bags needed = ceil(200 ÷ 12) = ceil(16.667) = 17 bags — despite laying fewer total units than the brick example, the block project needs more bags, since each block consumes far more mortar per unit than a brick does.
Questions
How many bricks does one 80lb bag of mortar lay?
A commonly cited typical figure is around 36 standard bricks per 80lb bag at a standard 3/8-inch joint width, but real coverage varies with the specific mortar product, brick size, and how thick your joints actually run — some sources cite ranges as wide as 36 to 65 bricks per bag depending on brand and brick dimensions. For a large or cost-sensitive project, check your specific mortar mix's packaging for its stated coverage rather than relying on a single generic number.
How many CMU blocks does one 80lb bag of mortar lay?
A commonly cited typical figure is around 12 standard 8×8×16-inch blocks per 80lb bag, though some sources put the range as high as 12 to 15 blocks per bag depending on the mortar brand and exact block dimensions. Since block mortar joints are proportionally larger relative to the unit than typical brick joints, blocks generally consume noticeably more mortar per unit than bricks do — which is why the same 80lb bag covers far fewer blocks than bricks.
Why does the calculator round up instead of a decimal bag count?
Because mortar mix is sold in whole bags — a supplier won't sell you 13.9 bags. Rounding up guarantees you have enough material to finish the job, accepting that the last bag will likely have some material left over. This is the same rounding convention used across bag-yield calculators for concrete, paint, insulation, and other materials sold in fixed package sizes.
Does joint width affect how many bricks a bag of mortar covers?
Yes, significantly. A thicker mortar joint uses more material per linear foot of brick coursing, so a project with wider-than-standard joints will get fewer bricks out of the same 80lb bag than the typical 36-brick figure assumes, while tighter joints stretch a bag further. If your project specifies a joint width noticeably different from the standard 3/8 inch, adjust your expected coverage rate accordingly rather than relying on the default.
Should I buy extra mortar mix beyond the calculated bag count?
It's common practice to add a small buffer beyond the bare calculated total, since real-world mortar usage includes some waste from mixing, spillage, and touch-up work, and running short mid-project to wait on another bag delivery is a bigger hassle than having one extra bag left over. This calculator already rounds up to a whole bag for the units you enter, but padding your order slightly further is a reasonable practical habit for a real job.