Calculator
Mortar Mix Calculator
A cubic foot of mortar joint looks like a geometry problem, and solving it that way under-orders badly. Multiply a brick's joint width by its face perimeter and you can work out how much mortar its vertical joints actually contain — but scaled up across a wall, that figure comes out at roughly a third of what a bag of pre-blended mortar is rated to lay. The gap is bedding: every unit sits in a full bed of mortar underneath it as well as the joints around it, and every trowel-load that lands on the board instead of the wall is mortar you bought and didn't lay.
This calculator does not try to out-guess that gap with a better geometry model. It starts from the published bag yield — bricks or blocks laid per 80 lb bag at a standard joint — and scales that figure for the joint width and bag size you're actually using, because the yield printed on a bag is a better number than anything this page could derive from the joint dimensions alone.
Calculate your quantity
Bricks or blocks, from the brick or block calculator.
Mortar dropped off the board is real and is not recoverable.
Mortar bags needed
15 80 lb bags
- Units per bag
- 37 bricks
- Joint width factor
- 1 x
- Before waste
- 13.51 bags
- Mixed mortar yield
- 9 cu ft
- Bag yields assume a 3/8 in joint, full bedding for brick and face-shell bedding for block.
Shopping summary
- • 15 x 80 lb bags of pre-blended mortar mix (0.6 tons total)
This is an estimate — confirm structural work with a professional.
How this calculation works
Brick and block start from different base yields, and the gap between them is not just size. Modular brick is laid at roughly 37 units per 80 lb bag; standard concrete block manages only about 12, despite covering far more wall per unit, because brick is normally set in a full mortar bed across its whole footprint while block is commonly laid with face-shell bedding — mortar only on the two outer webs of the block, not the hollow core between them. Both figures assume a 3/8 inch joint, which is the reference width the bag's printed yield is tested at.
Move off that reference joint and the yield scales. A 1/2 inch joint uses roughly a third more mortar per unit than 3/8 inch, so the units-per-bag figure drops by the same ratio — this page scales linearly from the one published data point, which is an approximation but the only defensible one without a second reference to interpolate between. Bag size scales the same way: a 60 lb bag holds three-quarters the mix of an 80 lb bag, so it lays three-quarters as many units.
- The joint-width scaling is linear from a single reference point (3/8 in), not measured at every width — treat it as a good working estimate, not a lab figure.
- Full bedding versus face-shell bedding is already baked into the 37-versus-12 base figures; there's no separate factor to apply for it.
- This is mortar for laying units. A scratch coat, a stucco base coat, and a stone veneer setting bed are different mixes with their own coverage figures on their own pages.
- Waste on mortar should run generous — unlike a cut brick, mortar that sets on the board before you get to it cannot be reclaimed and remixed.
The formula
bags = (units ÷ unitsPerBag) × (1 + waste); unitsPerBag = (baseUnitsPerBag × bagLbs ÷ 80) ÷ jointFactor; jointFactor = joint width ÷ 3/8 in
- baseUnitsPerBag
- The published units laid per 80 lb bag at a 3/8 in joint: 37 for brick, 12 for concrete block. A trade figure taken as given, not derived from geometry, because geometry undercounts by roughly a third once bedding and board losses are included.
- jointFactor
- Your joint width divided by the 3/8 in reference the base figure assumes. A wider joint raises this above 1 and lowers units per bag; a narrower one does the opposite.
- bagLbs
- The bag size you're actually buying, 60 or 80 lb. Scales the base yield proportionally — a 60 lb bag lays three-quarters as many units as an 80 lb bag of the same mix.
- units
- The count of bricks or blocks to be laid — normally the number the brick calculator or concrete block calculator just produced, carried over as this page's input.
- waste
- Percentage held back for mortar dropped off the board, batches mixed slightly rich, and the residue left in a bag that never fully scrapes out.
The published bag yield deliberately overrides the geometry here. Pure joint-volume arithmetic for modular brick at 3/8 inch works out to roughly 129 bricks per cubic foot of mortar, which back-converts to well over 100 bricks per 80 lb bag — nearly three times the 37 the trade actually gets. That gap is real mortar loss (bedding, droppings, mixing overage), not a mistake in the geometry, which is why this page starts from the bag figure instead of trying to correct the geometry with a fudge factor.
Where these numbers come from
- 37 bricks per 80 lb bag at a 3/8 in joint
- Trade-published figure printed on pre-blended mortar bags and widely quoted by masonry suppliers. Used directly rather than derived, because it already accounts for full bedding and normal handling loss that pure joint geometry does not.
- 12 blocks per 80 lb bag at a 3/8 in joint
- Same trade-published source, lower than brick's figure because a concrete block, even laid with only face-shell bedding, is a much larger unit and its two mortar webs still consume more mix per piece than a brick's joints do.
- Linear scaling from the 3/8 in reference joint
- Derived on this page, not looked up. Real mortar consumption tracks joint cross-sectional area more closely than joint width, but only one reference width is published for the base figures, so proportional scaling from that single point is the most defensible estimate available.
- 10% waste
- Trade convention for mortar mixing and application. Generous relative to a masonry unit's own waste allowance, because mortar that begins to set on the mortarboard is a total loss, not a reusable offcut.
Worked examples
1,200 bricks at a standard 3/8 inch joint
| Units to lay | 1200 |
|---|---|
| Unit type | Brick |
| Joint width | 0.375 in |
| Bag size | 80 lb bag |
| Waste factor | 10 % |
| Mortar bags needed | 36 80 lb bags |
|---|---|
| Units per bag | 37 bricks |
| Joint width factor | 1 x |
| Before waste | 32.43 bags |
| Mixed mortar yield | 21.6 cu ft |
At the reference joint width the joint factor is exactly 1, so the full 37-bricks-per-bag figure applies unscaled: 1,200 bricks divided by 37 is 32.4 bags before waste, and 10% waste rounds that up to 36. This is the case the published yield was measured for, so there's no scaling uncertainty stacked on top of the trade figure itself.
It's worth sitting with why 36 bags is right and a geometry-based estimate would not be. Pure joint volume for 1,200 bricks at 3/8 inch works out to well under half this bag count — the extra mortar is going under every brick as a bed and onto the board as loss, and both of those are real costs a wall-area calculation simply doesn't see.
800 concrete blocks at a thicker 1/2 inch joint, in 60 lb bags
| Units to lay | 800 |
|---|---|
| Unit type | Concrete block |
| Joint width | 0.5 in |
| Bag size | 60 lb bag |
| Waste factor | 10 % |
| Mortar bags needed | 131 60 lb bags |
|---|---|
| Units per bag | 6.8 blocks |
| Joint width factor | 1.33 x |
| Before waste | 118.52 bags |
| Mixed mortar yield | 58.95 cu ft |
Three factors compound here instead of one. Block already starts at a lower base yield than brick — 12 rather than 37 per 80 lb bag. Dropping to a 60 lb bag cuts that to 9. Widening the joint to 1/2 inch (a joint factor of 1.33) cuts it again, to 6.75 units per bag. The result is 131 bags for fewer than a thousand units, against 36 bags for 1,200 bricks in the first example — a near-fourfold difference in bags per unit laid, entirely from unit type, bag size and joint width rather than from wall size.
If this job's supplier only stocks 80 lb bags, re-run the figure at that size before ordering — bag size is not a rounding detail here, it's most of the reason this count is high. Buying against the 60 lb figure when you'll actually be handed 80 lb bags leaves a meaningful pile of unused mortar mix on site.
Common mistakes
- Working mortar volume out from joint geometry — width times bed thickness times joint length — instead of using the published bag yield. It under-orders by roughly a third because it ignores bedding and mixing loss entirely.
- Using the brick yield figure for a block job, or the reverse. The two figures differ by a factor of about three; swapping them either strands you a third of the way through a wall or leaves several unopened bags on site.
- Leaving the joint width at its 3/8 inch default when the actual job is matching an older wall at 1/2 inch or wider. That single field moves the bag count by a third or more — it's not a fine-tuning input.
- Ordering against a bag size the local yard doesn't actually stock. The count is specific to the bag weight entered; a supplier who only sells 80 lb bags will not sell you a partial bag to match a 60 lb calculation.
- Treating this page's output as covering a scratch coat, stucco base, or veneer setting bed. Those are different mixes with their own coverage rates on the stucco calculator and stone veneer calculator.
- Cutting the waste allowance on a hot, dry or windy day. Mortar that flashes off on the board before it's used is not a small loss on days like that, and the 10% default assumes ordinary conditions.
Shopping summary
The unit count this page wants is the finished, waste-included figure from the brick calculator or concrete block calculator — run that page first, then bring its total here rather than guessing a round number of units to be laid.
Order full bags; a yard will not split one, and the waste allowance already assumes you'll have some mix left over rather than run out mid-course. Sand for on-site mixing rather than pre-blended bags is a separate order this page doesn't cover, and its ratio depends on which mortar type your specification calls for.
FAQ
Why is the bag yield so much lower than what the joint volume alone would suggest?
Because the joint isn't where most of the mortar goes. Every brick or block also sits in a full or partial bed of mortar underneath it, and a working mason drops and discards mortar off the board through a normal day. Both are real consumption that a joint-volume calculation simply never counts, which is why this page uses the bag's own printed yield instead of deriving one from geometry.
Does joint width really move the bag count as much as this page suggests?
Yes — going from a 3/8 to a 1/2 inch joint is a third more mortar volume per lineal foot of joint, and that shows up directly as a third fewer units per bag. It's a bigger swing than most people expect from what looks like a small dimension change, and it's the reason joint width is a required field here rather than a fixed assumption.
Why does concrete block need so much less mortar per unit than brick, given how much bigger a block is?
Standard block is normally laid with face-shell bedding — mortar only along the two outer webs of the block's cross-section, not filling the hollow core — while brick is typically bedded fully across its face. A block covers far more wall per unit than a brick does, but it doesn't consume mortar in proportion to that size, which is why 12 blocks per bag and 37 bricks per bag aren't as far apart as the units' sizes alone would suggest.
Does the mortar type — Type N, S, or M — change how far a bag goes?
The published yield this page uses is for a standard pre-blended bag; that figure describes volume, and the mix type mainly changes strength and workability rather than the volume a bag produces. If your bag's own printed coverage differs from the figures here, use the number on your bag — supplier formulations vary more than the type designation alone predicts.
Should I round the bag count up to a full pallet before ordering?
It's worth asking your supplier what a pallet holds before you do — pallet counts vary by brand and region, and rounding to one only saves a trip if the price difference between a part-pallet and a full one makes it worthwhile. The waste allowance already gives you a small cushion either way.
I'm laying stone veneer, not brick or block — does this page apply?
No. Veneer stone is set with a different bedding method and a different coverage rate per square foot rather than per unit, and it's covered on the stone veneer calculator instead. This page's per-unit yield figures are specific to discrete brick and block.
Where to go next
The projects this number is a step of, the guides that explain the method behind it, and the rest of its trade group.