How many CMU blocks per square foot?

A standard 8×8×16 CMU (nominal) covers approximately 0.89 sq ft of wall face. That means you need about 1.125 blocks per square foot, or roughly 113 blocks per 100 sq ft. Add 5–10% for waste and cuts.

How much mortar do I need for CMU blocks?

Standard CMU construction uses approximately 1 bag of 70-lb mortar mix per 25 blocks, or about 3 bags per 100 sq ft of wall. Face shell bedding (standard) uses less mortar than full bedding.

When should CMU cells be grouted?

Cells are grouted when reinforcement is present (per MSJC Code), for increased structural capacity, or for bond beams. Partial grouting (every other cell) is common in residential retaining walls. Full grouting is used for high-load walls and seismic zones.

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CMU Block Calculator

Blocks, mortar, grout, and rebar for concrete masonry unit walls

0 Blocks needed

0 Mortar bags

0.0 Grout (yd³)

$0 Est. material cost

Wall Dimensions

Wall length

Wall height

Number of walls

Openings (doors/windows)

sq ft

Block Type

CMU size

Waste factor

Grout & Rebar

Cell grouting

Bond beams

Vertical rebar spacing

Results

0 blocks

0 Wall sq ft

0 Block courses

0 Blocks/course

0 Mortar bags (70 lb)

0.00 Grout (yd³)

0 Vert. rebar (ft)

Materials Breakdown

Course-by-Course Schedule

Bond beam courses are highlighted. Vertical rebar at every marked cell.

Unit Prices

CMU block (each)

Mortar mix (per 70-lb bag)

Grout (per yd³)

Rebar #5 (per lin ft)

2024 price ranges:
8×8×16 CMU: $2–$4/block · Mortar 70-lb: $10–$15
Grout: $150–$250/yd³ · Rebar #4: $0.40–$0.70/ft

Cost Breakdown

$0 total

$0 Blocks

$0 Mortar

$0 Grout

Cost Distribution

Standard CMU Sizes (Nominal)

Size (W×H×L)	Actual	Coverage/block	Blocks/100 sqft
4×8×16	3⅝×7⅝×15⅝	0.89 sqft	113
6×8×16	5⅝×7⅝×15⅝	0.89 sqft	113
8×8×16 ★	7⅝×7⅝×15⅝	0.89 sqft	113
8×8×8	7⅝×7⅝×7⅝	0.44 sqft	225
12×8×16	11⅝×7⅝×15⅝	0.89 sqft	113

★ Most common. Nominal includes ⅜ in mortar joint.

Mortar Types (ASTM C270)

Type	Compressive	Use
Type S	1,800 psi	Below grade, retaining walls — most common
Type M	2,500 psi	Heavy loads, severe exposure
Type N	750 psi	Above-grade, interior non-load-bearing

Grout Types (ASTM C476)

Type	Max aggregate	Use
Fine grout	⅜ in	Small cells, narrow collar joints
Coarse grout	½ in	Standard CMU cells, bond beams

MSJC / TMS 402 Reinforcement

Application	Vertical	Horizontal
Unreinforced bearing wall	—	Bond beam every 4 courses
Reinforced load-bearing	#5 @ 48 in max	#5 bond beam @ 48 in
Retaining wall (≤4 ft)	#4 @ 24 in	Bond beam @ base + top
Retaining wall (4–8 ft)	#5 @ 16 in	Bond beam every 4 courses
Seismic zone D/E	#5 @ 24 in	#5 bond beam every 2 courses

How to Use This Calculator

1Enter your wall length and height in feet. For L-shaped or multi-section walls, calculate each section separately and sum the results.

2Select your block size — standard 8×8×16 is used for most walls; 12×8×16 for thicker load-bearing or retaining walls; 4-inch for partitions.

3Choose your grouting option — no grout (non-structural), partial grout (every other core), or full grout (all cores filled for maximum strength and seismic resistance).

4Set vertical rebar spacing if applicable. The calculator outputs total rebar linear footage based on wall height and on-center spacing.

5Review the materials summary — block count (with waste), mortar bags, grout volume, and rebar quantities. Add 5–10% waste for complex walls with many corners and cuts.

Key Terms

CMU (Concrete Masonry Unit) — A hollow concrete block manufactured to ASTM C90 standards. Standard size is 8×8×16 inches (nominal), with actual dimensions of 7⅝×7⅝×15⅝ to allow for ⅜-inch mortar joints.

Bond Beam — A course of special U-shaped (open-top) CMU blocks that are grouted solid and contain horizontal rebar. Provides lateral strength and ties the wall together. Required at tops of walls and at specified intervals.

Face Shell Bedding — Mortar applied only to the outer shells (faces) of the block, not the webs. Standard practice for most CMU walls — uses less mortar and is faster than full bedding.

Full Mortar Bedding — Mortar applied to all surfaces including webs. Required for the first course on footings, for heavily loaded walls, and when specified by the structural engineer (MSJC Code).

Grouting — Filling block cores with fluid concrete (grout) to increase strength and allow rebar placement. Partial grouting fills only reinforced cores; full grouting fills every core for maximum load capacity.

ASTM C90 — The standard specification for loadbearing concrete masonry units. Specifies minimum compressive strength of 1,900 psi net area and dimensional tolerances. All structural CMU should meet C90.

Frequently Asked Questions

What's the difference between CMU and cinder block?

Cinder block is an older term for blocks made with coal cinders as aggregate. Modern CMU (concrete masonry unit) uses lightweight aggregates or normal-weight concrete. The terms are often used interchangeably in the field, but modern CMU has consistent ASTM C90 standards. Most residential and commercial construction now uses CMU.

Should I use face shell or full mortar bedding?

Face shell bedding (mortar only on the outer shells, not the webs) is standard for most CMU construction — it uses less mortar and is faster to lay. Full mortar bedding (all surfaces) is required for the first course on footings and for heavily loaded walls. MSJC Code specifies when full bedding is required.

How do I calculate CMU for a retaining wall?

Use this calculator with your wall dimensions. For retaining walls, partial or full grouting plus vertical rebar is typically required by code. For walls over 4 feet, engineered drawings are usually required. This calculator gives material quantities — consult a structural engineer for retaining wall design.

How long does it take to lay CMU blocks?

An experienced mason can typically lay 100–150 standard 8×8×16 blocks per day in straightforward conditions. Complex corners, bond beams, and heavily reinforced walls take longer. Factor in 1 day of setup/layout per project.