Construction Calculator
Mortar Calculator
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Work out the mortar a brick or block wall really takes — the volume left in the joints, the much larger amount a mason goes through, and the bags and sand that comes to.
Mortar Calculator
Mortar to order for brick and block
Product
0.707 ft³ — sand included
Results
Bags to buy
41
80 lb premix
Mortar to order
28.5 ft³
10.9 ft³ ends up in the joints
In the Joints Against What to Buy
Ordering the net joint volume would cover only about 38% of this wall. The difference is mortar furrowed, squeezed out and struck off, dropped and left on the board.
Two figures are given because they differ a great deal. 10.95 cu ft is the mortar left in the finished joints; 28.53 cu ft is what to buy. Ordering the net figure would cover only about 38% of the wall.
The ordering figure is calibrated to Quikrete’s published yield of about 144 standard bricks per 70 lb bag of masonry cement, which matches Titan America’s supplier rule of 7 bags per 1,000 modular brick. That yield excludes waste yet is about 2.4 times the net joint volume — the difference is mortar furrowed, squeezed out and struck off, dropped and left on the board.
At 6.550 bricks per square foot, each bag lays about 32 bricks at this rate, waste included.
Premixed mortar already contains its sand. The 80 lb yield of 0.707 cu ft is implied by Quikrete’s 37 bricks per 80 lb bag at the same per-brick consumption as their masonry cement.
This estimates quantity only. Mortar type — N, S or M — follows from exposure and structural requirements, and grout for filled cores or collar joints is a separate material not counted here.
Step-by-Step Calculation
Step 1 — Wall area
20 × 10 = 200.00 sq ft
Step 2 — Brick count
module = (8 + 0.375) × (2.25 + 0.375) = 21.9844 sq in
144 ÷ 21.9844 = 6.5501 per sq ft
200.00 × 6.5501 = 1,310.02 → 1,311
Step 3 — Net mortar in the joints
joint face per brick = 21.9844 − 18.0000 = 3.9844 sq in
mortar depth = brick depth 3.625 in
3.9844 × 3.625 = 14.443 cu in per brick
× 1,310.02 ÷ 1,728 = 10.950 cu ft
Step 4 — Mortar to order
consumption factor 2.368 (manufacturer yield ÷ net, 144 bricks per bag)
10.950 × 2.368 = 25.933 cu ft
+ 10% waste = 28.526 cu ft
Step 5 — Bags
Premixed mortar mix, 80 lb yields 0.7066 cu ft per bag
28.526 ÷ 0.7066 = 40.371 → 41 bags
Result — 1,311 bricks, 10.95 cu ft in the joints, order 28.53 cu ft (41 bags)
Mortar Is the Joint Around Each Brick
Each brick, plus half a mortar joint on every side, forms a repeating cell in the wall face. The cell area sets how many bricks fit in a square foot, and the part of the cell the brick does not fill, times the bed depth, is the mortar per brick.
The Joints Hold Less Than Half of What You Use
The obvious way to estimate mortar is to measure the joints: wall volume minus the volume of the bricks. For a 20 × 10 ft wall of standard brick at 3/8 in joints that gives 10.95 cubic feet — and that figure is right, as far as it goes. It is the mortar left in the finished wall.
It is not what you need to buy. Manufacturer yields — which both Quikrete and Titan America state exclude waste — put the mortar actually used on that wall at about 26 cubic feet, roughly 2.4 times the net volume. The difference is mortar spread thick and furrowed, squeezed out as each brick is set and struck off, dropped, and left on the board to stiffen.
So this calculator reports both. The net figure tells you what is in the wall; the ordering figure, calibrated to published yields, tells you what to buy. Ordering the net volume — even with a generous waste allowance — runs out well under halfway up.
Mortar Formulas
1. Units per Square Foot
2. Net Mortar in the Joints
3. Mortar to Order
4. Bags and Sand
Where the Consumption Factor Comes From
Published yields and the net joint volume of the same standard units, at 3/8 in joints:
| Source | Published yield | Implies |
|---|---|---|
| Quikrete Type N masonry cement | 70 lb + 240 lb sand = 2.75 cu ft; 144 brick or 46 block | 19.10 cu ft per 1,000 brick |
| Titan America supplier rule | 7 bags per 1,000 modular brick; 3 per 100 block | 143 brick per bag |
| Quikrete Mortar Mix, 80 lb | about 37 brick or 13 block per bag | 0.707 cu ft per bag |
| Net joint volume, modular brick | geometry, 7-5/8 × 2-1/4 × 3-5/8 | 8.06 cu ft per 1,000 |
The two brick sources agree to within 1% — 144 against 143 bricks per bag — and both run 2.37 times the mortar physically in the joints. That ratio is the consumption factor. For block, Quikrete's 46 blocks per bag against the face-shell net volume gives 4.66; the factor is higher because face-shell joints are narrow, so the fixed losses of spreading and striking weigh more heavily. Titan's 3 bags per 100 block is more conservative again. Applying the factor to the net volume of whatever unit you enter reproduces the published yields exactly for the standard units, and scales sensibly for others.
One honest wrinkle: Quikrete's own premix and masonry-cement figures imply slightly different brick-to-block ratios, so with premix this calculator lays about 11.8 blocks per 80 lb bag where the bag says 13. It errs about 10% on the generous side for block with premix.
Hollow Block Is Not Solid, and 16 × 8 Is Not 16 × 8
Two traps catch most block estimates. The first is face-shell bedding. Hollow block is normally laid with mortar on the two face shells only, so on an 8 in block the bed is about 2.5 in deep, not 7-5/8. Measuring it the brick way — wall volume less block volume — treats the block as solid and gives 10.56 cu ft for a 30 × 8 ft wall where the net is 3.46: about three times too much.
The second is nominal size. Masonry is named by its laid-out size including the joint. An "8 × 8 × 16" block is 7-5/8 × 7-5/8 × 15-5/8, which lays out at exactly 1.125 blocks per square foot. Entering 16 × 8 as the block and adding a joint on top gives 253 blocks for that wall instead of 270 — 6.7% short. The presets here carry actual dimensions, and the calculator warns if a block looks nominal.
Mortar per 100 Square Feet by Unit
At 3/8 in joints, block on face-shell bedding, before waste:
| Unit | Per sq ft | Net cu ft | Order cu ft | 80 lb bags |
|---|---|---|---|---|
| Modular brick | 6.857 | 5.53 | 13.10 | 18.5 |
| Standard brick | 6.550 | 5.47 | 12.97 | 18.4 |
| Queen brick | 5.760 | 4.20 | 9.95 | 14.1 |
| King brick | 4.800 | 3.95 | 9.34 | 13.2 |
| Utility brick | 3.000 | 3.69 | 8.73 | 12.4 |
| 4 in CMU | 1.125 | 0.87 | 4.04 | 5.7 |
| 6 in CMU | 1.125 | 1.15 | 5.38 | 7.6 |
| 8 in CMU | 1.125 | 1.44 | 6.73 | 9.5 |
| 12 in CMU | 1.125 | 1.73 | 8.07 | 11.4 |
Bigger units mean fewer joints per square foot, which is why block takes about half the mortar of brick for the same wall area. The face-shell figures assume typical shell thicknesses of 3/4 to 1-1/2 in — face shells vary between manufacturers, so measure the block you are buying.
Premix or Site-Mixed, and the Mix Ratio
Premixed mortar comes with its sand in the bag; an 80 lb bag makes about 0.71 cu ft. Site-mixed mortar uses a 70 lb bag of masonry cement — about one cubic foot — with sand added on site, and makes about 2.75 cu ft at 1:3. For the 20 × 10 ft brick wall that is 41 premix bags or 11 bags of masonry cement plus 33 cu ft of sand: the same mortar, a very different delivery.
The mix ratio is constrained. ASTM C270's proportion specification keeps sand between 2-1/4 and 3 times the cementitious volume, so 1:3 is the leanest conforming mix. A 1:4 mix is sometimes quoted to save cement, but it falls outside the standard and weakens both the mortar and its bond to the units. Richer mixes use more cement per cubic foot: on the example wall, 1:2.25 needs 13 bags against 11 at 1:3.
Example Calculations
A brick wall, a block wall, and the brick wall site-mixed with extra waste:
Example 1 — 20 × 10 ft Brick Wall, 3/8 in Joints
Standard 8 × 2-1/4 × 3-5/8 brick. The often-quoted 8–12 cu ft is the net figure.
Module = 8.375 × 2.625 = 21.98 sq in → 6.550 bricks per sq ft
200 sq ft × 6.550 = 1,310.02 → 1,311 bricks
Net mortar in the joints = 10.95 cu ft
Manufacturer consumption = 10.95 × 2.37 = 25.93 cu ft
With 10% waste: 28.53 cu ft = 41 × 80 lb premix bags
Ordering only 10.95 cu ft would run out about 38% of the way up
Example 2 — 30 × 8 ft Wall of 8 in Block
"16 × 8" is nominal; the block is 15-5/8 × 7-5/8 actual.
240 sq ft × 1.125 blocks per sq ft = 270 blocks
Face-shell bedding: mortar 2 × 1.25 = 2.5 in deep, not 7-5/8
Net mortar in the joints = 3.46 cu ft
Treated as solid, it would be 10.56 cu ft — about 3× too much
Manufacturer consumption = 16.14 cu ft, or 23 × 80 lb premix
Nominal sizes entered as actual give 253 blocks — 6.7% short
Example 3 — Example 1 With 15% Waste, Site-Mixed
Masonry cement and sand instead of premix bags.
Ordering volume 25.93 cu ft × 1.15 = 29.82 cu ft
One 70 lb bag of masonry cement at 1:3 makes 2.75 cu ft
29.82 ÷ 2.75 = 10.84 → 11 bags of masonry cement
Sand at 1:3 = 11 × 3 = 33 cu ft, about 2,640 lb
Against 43 × 80 lb premix bags for the same wall
Site mixing moves far less weight, but needs the sand delivered
Before You Order
Order against the mortar-to-order figure, not the net joint volume — the net figure is useful for understanding the wall but will run out well under halfway. Measure the actual size of the units you are buying rather than trusting the nominal name, and on block check the face-shell thickness, which varies between manufacturers. Confirm whether the block is to be face-shell or fully bedded; full bedding is normally limited to the first course, piers and grouted cells, and it roughly triples the net mortar per block. If you are site-mixing, have the sand delivered with some margin, since damp sand bulks and suppliers often allow nearly 4 cu ft per bag of cement. Keep the mix within 1:2-1/4 to 1:3 for a conforming mortar, and choose the type — N, S or M — from the exposure and structural requirements rather than from what is on the shelf. Mortar stiffens on the board, so mix in batches you can lay in about two hours. Grout for filled cores or collar joints is a separate material and is not counted here.
Frequently Asked Questions
- How much mortar do I need for a brick wall?
- Far more than the volume of the joints. A 20 × 10 ft wall of standard brick with 3/8 in joints holds 10.95 cu ft of mortar once finished, but manufacturer yields put the amount actually used at about 26 cu ft — roughly 2.4 times as much. With 10% waste that is 28.5 cu ft, or 41 bags of 80 lb premixed mortar. Ordering the net joint volume would run out well under halfway up the wall.
- Why is mortar consumption so much higher than the joint volume?
- Because a mason handles much more mortar than ends up in the wall. Bed joints are spread thick and furrowed, then squeezed down as the unit is set; the excess is struck off, some drops, and mortar left on the board stiffens and is discarded. Quikrete and Titan both publish yields that exclude waste, yet for modular brick they work out to 19.1 cu ft per 1,000 against 8.06 cu ft of mortar actually in the joints.
- How many bricks does a bag of mortar lay?
- About 144 standard bricks per 70 lb bag of masonry cement mixed with sand, or about 37 bricks per 80 lb bag of premixed mortar mix, according to Quikrete. Titan America's supplier rule of 7 bags per 1,000 modular brick works out to 143 per bag, agreeing almost exactly. These yields assume 3/8 in joints and exclude waste.
- How much mortar do I need per 100 concrete blocks?
- For 8 in block laid with face-shell bedding, Quikrete's yield of about 46 blocks per 70 lb bag of masonry cement works out to roughly 6 cu ft per 100 blocks, or just over 2 bags. Titan America's supplier rule of 3 bags per 100 block is more conservative. The net mortar in those joints is only about 1.3 cu ft per 100 blocks, because face-shell bedding puts mortar on the two face shells only.
- What is face-shell bedding?
- Laying hollow concrete block with mortar on the two face shells only, leaving the cross-webs dry. It is the normal practice for hollow block, and it means the mortar bed is about 2.5 in deep on an 8 in block rather than the full 7-5/8 in. Calculating block mortar as if the unit were solid — wall volume minus block volume — overstates the net mortar about three times. Full bedding is usually limited to the first course, piers and grouted cells.
- Is an 8 × 8 × 16 block really 8 × 8 × 16?
- No — that is the nominal size, which includes a 3/8 in joint. The block itself is 7-5/8 × 7-5/8 × 15-5/8. With joints it lays out to exactly 1.125 blocks per square foot. Entering the nominal size as if it were the actual block and then adding a joint undercounts the block by 6.7%, and the same trap applies to brick, where a "modular" brick is 7-5/8 in long.
- What mix ratio should I use for mortar?
- By volume, between 1 part cementitious material to 2-1/4 parts sand and 1 to 3. That is the range ASTM C270's proportion specification allows, so 1:3 is the leanest conforming mix. A 1:4 mix saves cement but falls outside the standard and weakens the mortar and its bond. The mortar type — N, S or M — is a separate decision that follows from exposure and structural requirements.
- How much sand do I need for masonry mortar?
- About 3 cubic feet per 70 lb bag of masonry cement at 1:3. Quikrete gives 240 lb of sand per bag for 2.75 cu ft of mortar, which is about 80 lb per cubic foot. Damp sand bulks, so suppliers often allow more — Titan America's rule of 1 cubic yard of sand per 7 bags works out to about 3.9 cu ft per bag.
- Does joint thickness change how much mortar I need?
- Substantially. On the 20 × 10 ft brick wall, going from 3/8 in to 1/2 in joints raises the net mortar from 10.95 to 13.89 cu ft — 27% more — even though it lays 78 fewer bricks. Going down to 1/4 in drops it to 7.69 cu ft. The manufacturer yields assume 3/8 in, which is the standard for both brick and block.
- What waste factor should I add for mortar?
- Around 10% on top of the manufacturer-based ordering figure, which already includes normal droppings and struck-off mortar. The larger 15–20% sometimes quoted is meant for net joint volume — and even that falls well short, since the net volume is less than half of what masons actually use. Adding a waste factor to the net figure is the most common way mortar orders come up short.