Block Mortar Calculator

One 80-lb bag lays up to 13 standard blocks; enter wall size or a block count for whole 60-lb or 80-lb bags.

Estimate Block Mortar

Length (ft)

Height (ft)

Bag size:

Current mortar order

16 x 80-lb

180 base blocks / 13 blocks per bag + 10% order buffer

More options

Unit:

80-lb Coverage (blocks per bag)

60-lb Coverage (blocks per bag)

Use the coverage printed on the product you will buy.

Order Buffer10%

Cost Estimation

How many blocks will one bag of mortar lay?

One 80-lb bag lays up to 13 standard 8-inch (8x8x16) blocks; one 60-lb bag lays 9 (manufacturer coverage, linked below). A 12-blocks-per-bag rule of thumb is 9 bags for 100 blocks; at the labeled 13, 100 blocks is 8 bags before any order buffer.

Blocks to lay	80-lb bags	80-lb bags with 10% buffer	60-lb bags
100	8	9	12
200	16	17	23
500	39	43	56
1,000	77	85	112

Every row is produced by the calculator above at the default coverage, so the table and the tool always agree.

What does that mean per square foot or square metre?

A 100 sq ft wall works out to 113 standard blocks, or 9 80-lb bags before any order buffer.
A 10 m² wall works out to 122 standard blocks, or 10 80-lb bags before any order buffer.

Both figures use the same nominal 8 x 16 inch face module, so switching units does not change what you buy. Openings, half blocks, corners, and non-standard faces are not deducted; enter your own takeoff count when the wall is not a plain rectangle.

Treat these as planning figures for standard blockwork with a 3/8-inch joint. A bag stated in kilograms, a different block face, or a different joint profile changes the coverage, so re-run the calculator with the number printed on your bag.

Which CMU joints does this estimate cover?

The bag estimate covers the horizontal bed joints and vertical head joints used to lay standard hollow CMU. The labels show that boundary without relying on color.

Bed joint: included
Head joint: included
Hollow core
Core fill: excluded

Covers standard CMU bed and head joints only; grout or concrete core fill belongs in the block fill calculator. The diagram explains quantity scope — not structural design or mortar-type approval.

How do block counts become mortar bags?

Three steps: multiply blocks by your order buffer, divide by the blocks-per-bag coverage, and round up — mortar is sold by the whole bag.

Wall to blocks: base blocks = round up(wall area x face-module rate)
Blocks to bags: coverage target = round up(base blocks x (1 + order buffer %)); bags = round up(coverage target / product coverage)

In wall mode, the calculator turns wall area into a block count with the nominal 8 x 16 inch face module, which already includes the mortar joint. Already have a takeoff? Enter the whole-block count instead.

A pre-mix bag is a complete product. Masonry cement needs job-site sand, so the two bag counts cannot be compared directly. About 7 masonry-cement bags per 100 blocks is not the same order as 8 pre-mix 80-lb bags at 13 blocks per bag.

Product yield, block geometry, head joints, and joint profile can change the answer. Use the coverage printed for the product you will buy.

It does not include brick, pointing, thinset, AAC, stone, pavers, core fill, site-mix recipes, or structural design, and it does not total Portland cement, lime, or masonry sand. Names vary: concrete block, cinder block, concrete masonry unit, CMU, and blockwork describe the same wall; mason mix and spec mix are product names. Read the coverage, not the name.

What do two reproducible mortar orders look like?

These cases show the full path from a wall or an existing block takeoff to whole-bag purchasing. Every output uses the same calculation and default coverage as the live tool.

These are illustrative planning cases, not customer results.

12 × 4 ft garden divider

A short non-retaining garden divider needs a first mortar order before the crew starts laying block.

Inputs: 12 × 4 ft wall; wall-dimensions mode; 10% order buffer; 80-lb bag; 13 blocks per bag.
Reproducible output: 48 sq ft → 54 base blocks → 60 buffered blocks → 5 whole bags. Without the buffer: 5 bags.
Why this result: The 48 sq ft wall rounds up to 54 blocks. The 10% buffer raises the target to 60; at 13 blocks per bag, that rounds up to 5 whole bags.
What it means on the job: Without the buffer: 5 bags. With it: 5. Whole-bag rounding can absorb a small buffer, so you may gain capacity at no extra bag.
Use when: Use for standard CMU with a standard 3/8-inch joint and verified packaged-product coverage. It excludes core fill, retaining-wall design, and structural approval.

100-block takeoff

A small crew already has a 100-block takeoff and needs to turn that count into an 80-lb mortar order.

Inputs: 100 blocks from an existing takeoff; block-count mode; 10% order buffer; 80-lb bag; 13 blocks per bag.
Reproducible output: 100 base blocks → 110 buffered blocks → 9 whole bags. Without the buffer: 8 bags.
Why this result: The 10% buffer raises 100 blocks to 110. At 13 blocks per bag, that rounds up to 9 whole bags — versus 8 without the buffer.
What it means on the job: The buffered 9-bag order beats running short and making another supplier trip. Treat it as a planning allowance, not a promise that every bag yields the default coverage.
Use when: Use for a whole-block takeoff of standard CMU with a standard 3/8-inch joint and verified packaged-product coverage. It excludes core fill, site-mix recipes, and structural design.

Does mortar type change the bag count?

Types O, N, S, and M are specification classes under ASTM C270. Changing the letter does not change the bag count because quantity comes from the product coverage.

Type	Explanatory boundary
O	A lower-compressive-strength class with limited uses. The project documents must say when it is suitable.
N	A medium-compressive-strength class often specified for general unit masonry. This page does not decide whether it fits the wall.
S	A higher-compressive-strength and higher-bond-strength class. Structural and exposure requirements belong in the project specification.
M	The highest-compressive-strength class in this table. Its name is not a reason to substitute it for the specified mortar.

Use the mortar type and property or proportion specification named in the plans, project specifications, and local code. Do not use this table as structural design advice, and do not alter a packaged product with a site-mix recipe to imitate another type.

Where do these coverage numbers come from?

Manufacturer-stated coverage: QUIKRETE Mason Mix #1136 — an 80-lb bag lays up to 13 standard blocks; Sakrete Mortar Mix Type N — a 60-lb bag lays 9 blocks. The 3/8-inch joint assumption comes from a separate QUIKRETE block-wall guide, not from either yield statement. Sources checked August 3, 2026.

Update log: The Concrete Block Calculator site operator checked the linked product sheets, coverage labels, examples, FAQ, and scope on August 3, 2026.

Questions before you order

How many bags of mortar do I need per 100 blocks?

For 100 standard 8-inch (8x8x16) blocks, the 80-lb default of 13 blocks per bag rounds up to 8 whole bags. The common 12-blocks-per-bag shortcut is 9 bags for the same 100. With a 10% order buffer, 110 covered blocks round up to 9 bags. Actual bag needs change with product coverage, block geometry, and joint profile, so use the coverage stated for the product you will buy.

What should I enter if the bag does not list blocks per bag?

Check the product data sheet or ask the manufacturer or supplier for coverage for your block and joint profile. Keep the field editable rather than treating a planning default as a product guarantee.

Can I compare pre-mix bags with masonry cement bags?

Not by bag count alone. Pre-mix includes the dry ingredients for that product, while masonry cement is combined with job-site sand under a specified mix. That is why a masonry-cement takeoff of about 7 bags per 100 blocks is not 8 pre-mix 80-lb bags. Compare the manufacturer's yield and the project specification for the system you will use.

What should I do with the extra capacity on a small project?

Check whether the required mortar is sold in a smaller package and confirm the minimum practical order with the supplier. Extra capacity describes unopened product. Do not plan to store mixed mortar for later work.

My mortar is sold in 20 kg or 25 kg bags. Can I still use this?

Yes, but replace the coverage first. The 60-lb and 80-lb labels describe the two default products, while the calculation only uses the blocks-per-bag value you enter. Find the blocks per bag stated for your kilogram bag, type it into the coverage field, and read the result as that bag size. Metric wall dimensions already use the same physical face module, so unit switching alone does not change the order.

For the same standard CMU wall, continue with the calculator that owns the next task: