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Mortar Calculator

Volume from geometry, checked against the bag's own two claims

An 80 lb bag of mason mix claims 37 bricks or 13 blocks. Work both back through the geometry and they imply mortar volumes that differ by nearly a factor of two. They cannot both be right, and the bag does not say which bedding it assumed.

Mortar takeoff

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Mortar volume is computed from your unit size and joint rather than read off a bag. Unit dimensions are yours because ASTM C216 and C90 set them and neither is free to read.

Specification summary

Generated from on . Reopen that address to reproduce these figures exactly.

Entered

Result

This figure is drawn from the unit you type in above.
Where the mortar goes, in plan

Worked example

300 square feet of brickwork in 7-5/8 by 2-1/4 by 3-5/8 in brick with the code 3/8 in joint, full bedded.

  1. The cell is 8.00 by 2.63 in, so 6.86 bricks per square foot and 2,058 bricks in 300 sq ft.
  2. The mortar is the cell minus the brick. 8.00 x 2.63 x 3.625 is 76.1 cubic inches of cell; the brick is 62.2. So 13.93 cu in per brick, which is 16.59 cubic feet over the wall, or 19.08 with a 15% allowance.
  3. Now check that against the bag. Quikrete's 80 lb Mason Mix claims 37 bricks or 13 blocks. At this geometry 37 bricks needs 0.298 cu ft of mortar.
  4. And 13 blocks, face shell bedded, needs 0.164. Same bag, and the two claims imply mortar volumes that differ by 1.8 times. One of them is describing a different bedding or a different unit, and the bag does not say which.
  5. Bedding is the biggest variable on this page. A block full bedded takes 67.6 cu in against 21.8 face shell bedded, 3.1 times as much, and which one you get is a word nobody writes on the order.

Work the volume from your own unit and your own joint. The bag figure is a useful cross-check and a poor answer, because it cannot tell you which of its own two numbers applies to what you are laying.

The formula

Full bedding is a subtraction. Face shell bedding is not:

full = (l + j)(h + j)d − lhd    shell = 2sj(l + h)
l, h, d
the unit's own length, height and depth, measured
j
the mortar joint, 3/8 in per IRC R606.3.1
s
the face shell width, where the unit is bedded on its shells only
2sj(l + h)
two bed strips and two head strips, which is all the mortar there is

The two are not close on a hollow unit, because full bedding fills the webs and the cells and face shell bedding does not go near them. On a standard block the ratio is about three to one, which makes bedding method the single largest variable in a mortar order and the one least likely to be written down.

The bag's two coverage figures cannot both be right

Quikrete's 80 lb Mason Mix bag states 37 bricks or 13 blocks. Both figures are on the same product and this page takes them seriously enough to check them.

At a standard brick with a code joint, full bedded, 37 bricks needs 0.298 cubic feet of mortar. At a standard block face shell bedded, 13 blocks needs 0.164. The two differ by a factor of 1.8, so at most one of them describes the mortar actually in the bag.

The likely explanation is bedding, and the bag does not mention it. If the block figure assumed full bedding it would need 0.51 cu ft, which is further away still. Somewhere between the two there is a set of assumptions that reconciles them, and none of those assumptions is printed.

So this page computes from geometry and shows the bag figures beside it. That way you can see which of the two your job resembles, rather than picking a number and hoping. Unit dimensions are yours for the same reason: ASTM C216 and C90 set them and neither is free to read.

And the waste allowance here is larger than elsewhere on this site, deliberately. Mortar is mixed in batches, it goes off, and a meaningful fraction ends up on the board and the ground rather than in the wall. Fifteen percent is the default and it is not generous.

Prices for masonry units and mortar

The published figures for masonry units and mortar are on the block calculator, with the byline, the publication date and the caveats that go with them. They are not repeated here, because the same table on two pages is worth less than one table you can find.

This site publishes no price of its own. Why, and what that means for these figures.

Mortar is supposed to be the weak part

This is the thing most people have backwards, and it decides which type you should be buying.

ASTM C270 Type S is 1,800 psi and Type N is 750. Stronger sounds better. It usually is not.

Mortar is meant to be weaker than the units it joins. A wall moves, and when it does the stress has to go somewhere. If the mortar is the weaker material the crack runs along the joint, where it can be raked out and repointed for the cost of a morning. If the mortar is stronger, the crack runs through the brick, and there is no repair for that short of replacing units.

Which is why Type N is the usual choice for ordinary above-grade walls, and why Type S turns up where there is real structural demand: below grade, in retaining work, in high wind or seismic areas. Using S everywhere because it is the stronger number is a common and expensive instinct.

The block calculator on this site carries the full C270 table and the strengths that go with each type.

Why the waste allowance is bigger here

Fifteen percent is the default on this page against ten on most of the others, and it is not padding.

Mortar has a working life measured in hours. It is mixed in batches sized for how fast the wall is going up, and a batch that outlives its board goes in the barrow. Nobody mixes exactly enough, because running out mid-course is far worse than mixing a little over.

And a real amount of it never reaches the wall. It is squeezed out of every joint as the unit is pressed down, which is the code's own instruction in R606.3.2: units are placed with enough pressure to extrude mortar from the joint. What extrudes gets struck off, and most of it does not go back in the mix.

Then the joints themselves are finished. Tooling a joint compresses and removes material, and a raked or recessed joint removes considerably more than a struck one.

None of that is waste in the sense of a mistake. It is how the material is used, and a takeoff that assumes every cubic inch mixed ends up between two units will come up short on a real wall.

Frequently asked questions

How much mortar do I need per brick?
Work it from the geometry: the cell one brick occupies, minus the brick. On a 7-5/8 by 2-1/4 by 3-5/8 in brick with a 3/8 in joint that is 13.93 cubic inches, so about 125 bricks to the cubic foot of mortar. There is no universal figure because brick sizes differ.
How many bricks does a bag of mortar lay?
Quikrete's 80 lb Mason Mix says 37 bricks or 13 blocks. Worth knowing before you rely on it: worked back through the geometry those two claims imply mortar volumes 1.8 times apart, so at most one describes what is in the bag. The likely reason is that they assume different bedding, and the bag does not say.
What is face shell bedding?
Mortar laid only on the two face shells of a hollow unit rather than across the whole bed, leaving the webs and cells dry. It is the normal way to lay block, and it uses about a third of the mortar full bedding does. On a standard block that is 21.8 cubic inches against 67.6.
Type N or Type S mortar?
Type N for ordinary above-grade work, Type S where there is real structural demand: below grade, retaining walls, high wind or seismic areas. The instinct to buy the stronger one everywhere is usually wrong, because mortar is supposed to be weaker than the units so that cracks run in the joints where they can be repointed.
How much mortar waste should I allow?
Fifteen percent is this page's default, which is more than the ten used elsewhere on the site. Mortar has a working life of hours so batches are mixed generously, and the code itself requires enough pressure to extrude mortar from every joint, which is material that leaves the wall by design.
Does the joint size change the mortar much?
Substantially, because the mortar volume is the difference between two nearly equal numbers. Going from a 3/8 in joint to 1/2 in on a standard brick raises the mortar per unit by roughly a third, while raising the brick count by only a few percent. Small changes to the joint move the mortar order much more than they move the brick order.
Why does this page ask me to measure the brick?
Because ASTM C216 and C90 set unit dimensions and neither standard is free to read, so publishing a figure here would be citing something nobody can check. Brick and block sizes also vary by manufacturer more than people expect. Measuring one takes ten seconds and makes the answer yours.

Check these numbers yourself

How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.

Figures on this page last checked against the source documents on 2026-09-09. Codes are amended locally; confirm against the edition your jurisdiction enforces.

Related calculators

Unit dimensions are yours, measured. ASTM C216 and C90 set them and neither is free to read. The bag coverage figures shown are the manufacturer's own and this page checks them against your geometry rather than trusting them, because the two figures on one bag do not reconcile. Bedding method is the largest variable here and it is a decision made on site, so confirm it before ordering.