Concrete Block Calculator
Estimate CMU blocks and mortar for your block wall
Total length of the block wall
Height of the block wall
Standard CMU: 16"
Standard CMU: 8"
Standard joint thickness: 0.375" (3/8")
Blocks Needed
—
blocks
Mortar Bags
—
bag
Wall Area
—
sq ft
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Building a concrete block (CMU) wall? Accurate block and mortar estimates prevent shortages mid-project. Our calculator uses nominal block dimensions plus mortar joint thickness for a reliable count.
- Measure the total length and height of your wall in feet
- Confirm your block dimensions (standard CMU is 16" x 8")
- Enter the mortar joint thickness (3/8" is standard)
- The calculator adds a 5% waste factor for cuts and breakage
Expert Insights
Smart analysis for your Concrete Block project
Block Sizing Accuracy
Standard CMU blocks are 16" x 8" nominal, but actual dimensions are 15.625" x 7.625". The calculator uses your exact inputs for precise counts.
Mortar Yield per Bag
One 80 lb bag of premixed mortar lays roughly 14 standard blocks. Wider blocks (10" or 12") require more mortar per block.
Reinforcement Reminders
Walls over 4 ft tall typically need vertical rebar and grout-filled cells at 24-48" on center for structural integrity.
Calculation Formula
Effective width = Block length + Mortar joint (in)
Effective height = Block height + Mortar joint (in)
Blocks per sq ft = 144 / (Effective width x Effective height)
Wall area = Wall length x Wall height (sq ft)
Blocks = ceil(Wall area x Blocks per sq ft x 1.05) (5% waste)
Mortar bags = ceil(Blocks / 14)
Concrete Block Material Comparison
| Block Type | Dimensions (in) | Blocks/sq ft | Mortar Bags/100 | Typical Use |
|---|---|---|---|---|
| Standard CMU | 16 x 8 | ~1.125 | 8 | Foundation, walls |
| Half Block | 8 x 8 | ~2.25 | 16 | Corners, ends |
| Bond Beam | 16 x 8 | ~1.125 | 8 | Horizontal rebar |
| Slump Block | 16 x 6 | ~1.5 | 10 | Decorative walls |
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- National Concrete Masonry Association (NCMA) — TEK Notes & Masonry Design Manuals. Learn more
- American Concrete Institute (ACI) — ACI 530: Building Code Requirements for Masonry Structures. Learn more
- International Building Code (IBC) — Chapter 21 — Masonry. Learn more
Frequently Asked Questions
How many concrete blocks do I need per square foot?
A standard 8" x 16" CMU block with a 3/8" mortar joint covers about 1.125 blocks per square foot of wall area.
How many blocks can one bag of mortar lay?
One 80 lb bag of premixed mortar lays approximately 14 standard 8" x 16" concrete blocks.
What is the standard size of a concrete block?
The standard CMU (concrete masonry unit) is 16" long x 8" high, with nominal widths of 4", 6", 8", 10", or 12". The 8" wide block is the most common for structural walls.