Block Mortar Calculator
Find how many bags of mortar you need for a concrete block wall.
Tell us about your wall
Your answer
To lay 95 blocks (8 in), with 15% extra mortar.
Or mix your own
3 bags of masonry cement (70 lb) and 720 lb of mason sand. That is about 63 shovels, if damp, loose sand weighs 80 lb a cubic foot (CMHA).
This answer is a guide. For walls that hold weight or hold back soil, check your local building rules or ask a builder or engineer.
What it costs
Type N: $10.80, the middle of only 3 stores. Type S: $9.59, the middle of 7 stores (Oct 2026). An 8 in block: $2.84, the middle of 4 stores. We found too few brick prices to give one.
Quick answers
- 100 blocks (8 in)
- Bag counts give 8 bags of 80 lb mix. Add 15% for waste and buy 10.
- Water for 100 blocks
- About 50 quarts (12.5 gallons) for those 10 bags, at about 5 quarts a bag.
- 8 in blocks per bag
- Up to 13, says Quikrete. Sakrete says 12.
- 12 in blocks
- SPEC MIX says 9–11 per bag. We use 9, so 11.1 bags per 100 blocks.
- Which type?
- Most block walls above ground: Type N. Walls that hold weight or sit below ground: Type S. Foundation and retaining walls: S or M.
How to work it out
- Work out the square feet of wall: length × height.
- Multiply by 1.125 blocks per sq ft. Add 5% for broken blocks, and round up.
- Divide by how many blocks one bag lays for your width (see the table).
- Add 15% for waste if the count has none (8 in). Buy whole bags.
Wall: 20 × 4 = 80 sq ft
Blocks: 80 × 1.125 × 1.05 = 94.5 → 95
Mortar: 95 ÷ 12.5 = 7.6 bags
Plus 15%: 7.6 × 1.15 = 8.74 → 9 bags
Bags per 100 blocks, by width
Mortar types, water and sand are covered on the main mortar calculator page.
Widths run from 4 to 12 in. Two bag makers, SPEC MIX and TCC, say one bag lays fewer wide blocks than narrow ones.
| Width | SPEC MIX | TCC | We use | Bags per 100 |
|---|---|---|---|---|
| 4 in | 14–16 | 16 | 14 | 7.1 |
| 6 in | 11–13 | — | 11 | 9.1 |
| 8 in | 10–12 | 11–12 | 12.5 | 8 |
| 10 in | 10–12 | — | 10 | 10 |
| 12 in | 9–11 | 10 | 9 | 11.1 |
Bags per 100 has no extra. For 8 in we use 12.5, between Sakrete's 12 and Quikrete's 13.
For 8 in blocks, that is 8 bags per 100. Our concrete block calculator plans 8 too, so the two agree.
The calculator adds 15% for waste to the 8 in count. The other widths use SPEC MIX's counts, which have waste built in. So it starts those at 0%.
Does width matter? Not to CMHA
CMHA, a concrete masonry trade group, disagrees with the bag makers. Its estimates put mortar only on each block's outer edges, called face shells. So block width drops out.
CMHA says one bag lays about 16 blocks of any width. That count includes some waste. It comes to 6.25 bags per 100 blocks.
Lehigh, a cement maker, uses one figure for 4, 6, 8 and 12 in blocks, with no waste. It is 9 cubic feet of mortar per 112.5 blocks. That works out to about 9.4 blocks per bag, or 10.7 bags per 100.
So for 100 blocks, 8 in wide: CMHA says 6.25 bags, with waste in. Bag makers say about 8. Lehigh's figure, with no waste, gives about 10.7. We go with the bag makers.
Blocks per square foot
A block's face is 8 × 16 in, with its joint. A square foot is 144 square inches. So 144 ÷ 128 = 1.125 blocks per sq ft, for any width.
That is 112.5 blocks per 100 sq ft. CMHA adds 5% for broken blocks, which makes 119.
Don't add the extra twice. If you start from 119, the 5% is already in. The same goes for mortar counts that include waste.
Which type, and mixing your own
Type N suits most block walls above ground. Walls that hold weight call for S, says BIA. For foundation walls, CMHA's rule is Type M or S.
Retaining walls are less clear. BIA (for brick) picks M first. The ASTM table picks S first. For walls that hold back soil, check your local building rules or ask a builder or engineer.
The calculator starts on the Type S price, $9.59 a bag (7 stores, Oct 2026). That is just a starting price, not a rule. Pick N or S in step 3.
Masonry cement and sand
The counts differ here too. Quikrete says one 70 lb bag, with 240 lb of sand, lays about 46 blocks. CMHA says about 30.
For 100 blocks, that is 2.2 bags by Quikrete's count, or 3.3 by CMHA's. The calculator works it out from the mortar you need, so it may differ a little from both.
Its shovel count uses CMHA's figures. Sand weighs about 80 lb a cubic foot, and that is 7 shovels.
Questions people ask
How many bags of mortar per block?
For 8 in blocks, Sakrete says 12 per bag and Quikrete up to 13. Other makers say 10 to 15. At our 12.5, each block takes about 0.08 of a bag.
How many bags of mortar per 100 blocks?
About 8 bags for 8 in blocks. With 15% for waste, that is 9.2, so buy 10.
How many 8 inch blocks per bag of mortar?
Quikrete says up to 13 and Sakrete says 12. SPEC MIX says 10–12. CMHA, a trade group, says about 16.
How many bags of mortar per 12 inch block?
For 100 blocks, 12 in wide, plan about 11.1 bags. That uses SPEC MIX's low end. TCC's count gives 10 bags.
How much sand and mortar to lay block?
Bagged mortar mix has the sand in it. To mix your own for 100 blocks (8 in), plan 3 bags of masonry cement and 720 lb of sand.
How do I calculate mortar for a block wall?
Multiply the wall's square feet by 1.125 for blocks. Divide by the blocks one bag lays. Add 15% for waste if the count has none, and round up.
What mortar type is best for concrete block?
It depends on the wall. N suits most walls above ground. Use S for walls that carry weight or are below ground, and S or M for foundations. Check your local building rules or ask a builder or engineer.
Where our numbers come from
- Blocks, mortar, sand and core fill: Concrete Masonry & Hardscapes Association (TEK 04-02A)
- Block size: Concrete Masonry & Hardscapes Association (TEK 02-02B)
- Foundation walls need Type M or S: Concrete Masonry & Hardscapes Association (TEK 09-01A)
- Mortar per block: Quikrete Mortar Mix data sheet
- Mortar per block: Sakrete Type S bag (about 12 blocks per 80 lb bag)
- Bricks and blocks per bag by size: SPEC MIX data sheet (counts include waste)
- Blocks per bag by width: TCC Materials table (2025)
- Mortar bags per pallet: Quikrete Mortar Mix product page (80 lb: 42)
- Sand per bag of masonry cement: Lehigh White Masonry Cement data sheet
- Mortar per bag: Amerimix AMX 500 data sheet (80 lb makes about 0.78 cubic feet)
- Mortar per bag: Mutual Materials DesignMix data sheet (about 0.74 cubic feet)
- Mortar per bag: TCC Materials Tech-Mix Type S data sheet (about ¾ cubic foot)
- Mix your own mortar: Quikrete Masonry Cement data sheet (1 bag + 240 lb sand)
- Bricks per square foot and mortar waste: Brick Industry Association (TN 10)
- Which mortar type: Brick Industry Association (Technical Note 8B)
- Type N mortar: Sakrete data sheet (above ground only)
- Type N mortar price: the middle of 3 stores, 80 lb bag (Oct 2026)
- Block and mortar prices: the middle of 4 stores (blocks) and 7 stores (mortar), Oct 2026
- Brick prices seen: 2 US stores, $0.74–1.30 a brick (Oct 2026; too few for a default)
Made by BuildersCount. Last checked 3 Oct 2026.
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