Concrete Block Calculator
Calculate CMU blocks, mortar, and rebar needed for walls. Supports standard, half, and corner blocks with waste factor.
Wall Dimensions
Reinforcement Options
Related Calculators
About This Calculator
The Concrete Block Calculator determines exactly how many CMU (concrete masonry units) you need for any wall project—from foundation walls and retaining walls to garage buildings and privacy fences. Also commonly called cinder blocks or concrete blocks, these durable units form the backbone of masonry construction worldwide.
Our calculator accounts for wall dimensions, block size, mortar joints, door and window openings, and waste factors to provide accurate material estimates. We also calculate mortar bag requirements, rebar quantities for structural walls, and grout needs for filled cores. Whether you're a contractor bidding a commercial project or a homeowner planning a DIY garden wall, accurate block estimation prevents costly material shortages and expensive over-ordering.
Enter your wall dimensions, select your block specifications, and get a complete materials list with 2026 cost estimates. The calculator handles standard 8", 10", and 12" blocks, specialty blocks for corners and bond beams, and provides professional-grade quantity takeoffs trusted by masonry contractors.
How to Use the Concrete Block Calculator
- 1Enter the total wall length (combine all wall sections if building multiple walls).
- 2Enter the wall height in feet or specify the number of courses (each course is 8 inches).
- 3Select your block size: 8", 10", or 12" width based on structural requirements.
- 4Specify door and window openings to subtract from the total block count.
- 5Toggle mortar calculation to see bag requirements for your joint size.
- 6Enable rebar options for structural walls requiring reinforcement.
- 7Add grout calculations if filling cores for strength or waterproofing.
- 8Review the complete materials list with quantities and cost estimates.
Standard CMU Block Sizes and Coverage
Concrete blocks come in standard sizes based on nominal dimensions (which include the 3/8" mortar joint):
Common CMU Dimensions:
| Block Type | Actual Size | Nominal Size | Weight | Blocks/100 SF |
|---|---|---|---|---|
| 4" Standard | 3-5/8" × 7-5/8" × 15-5/8" | 4" × 8" × 16" | 26 lbs | 112.5 |
| 6" Standard | 5-5/8" × 7-5/8" × 15-5/8" | 6" × 8" × 16" | 32 lbs | 112.5 |
| 8" Standard | 7-5/8" × 7-5/8" × 15-5/8" | 8" × 8" × 16" | 38 lbs | 112.5 |
| 10" Standard | 9-5/8" × 7-5/8" × 15-5/8" | 10" × 8" × 16" | 43 lbs | 112.5 |
| 12" Standard | 11-5/8" × 7-5/8" × 15-5/8" | 12" × 8" × 16" | 52 lbs | 112.5 |
Block Coverage Formula:
- Standard blocks: 1.125 blocks per square foot of wall
- Each block covers 0.89 sq ft (with 3/8" mortar joints)
- 112.5 blocks per 100 square feet of wall area
Specialty Blocks:
| Type | Use Case | Nominal Size | Notes |
|---|---|---|---|
| Half Block | Corners, around openings | 8" × 8" × 8" | One flat end |
| Corner Block | Wall ends | 8" × 8" × 16" | Two finished ends |
| Bond Beam Block | Horizontal reinforcement | U-shaped, 8" × 8" × 16" | Holds rebar and grout |
| Lintel Block | Above door/window openings | U-shaped, laid on side | Structural support |
| Solid Cap Block | Top of walls | 8" × 4" × 16" | Flat solid top |
| Pilaster Block | Column integration | 16" × 8" × 16" | Extra wide |
| Scored/Split Face | Decorative walls | Various | Textured finish |
Mortar Requirements and Types
Mortar holds blocks together and fills the joints between courses:
Mortar Coverage per Bag:
| Bag Size | Mix Type | Blocks Laid | Wall Area |
|---|---|---|---|
| 60 lb bag | Pre-mixed | 12-15 blocks | ~12 sq ft |
| 80 lb bag | Pre-mixed | 15-20 blocks | ~15 sq ft |
| 94 lb bag | Portland cement | 18-24 blocks | ~20 sq ft |
Mortar Mix Types (ASTM C270):
| Type | Compressive Strength | Best Applications |
|---|---|---|
| Type N | 750 PSI | Above-grade, general purpose, non-load bearing |
| Type S | 1,800 PSI | Below-grade, retaining walls, wind/seismic zones |
| Type M | 2,500 PSI | Foundations, heavy loads, contact with soil |
| Type O | 350 PSI | Interior, non-load bearing only |
Mortar Mix Ratios (by volume):
| Type | Portland Cement | Lime | Sand |
|---|---|---|---|
| Type N | 1 | 1 | 6 |
| Type S | 1 | 0.5 | 4.5 |
| Type M | 1 | 0.25 | 3.5 |
Estimating Mortar Quantities:
- Standard rule: 8-9 bags (60 lb) per 100 standard blocks
- Add 10% for waste and joint variations
- Below-grade work typically uses more mortar
- Cold weather work may require extra due to slower setting
Joint Dimensions:
- Standard bed joint: 3/8" thick (horizontal)
- Standard head joint: 3/8" wide (vertical)
- Tooled joints (concave or V) improve weather resistance
- Raked joints look decorative but reduce weather resistance
Rebar and Grouting for Structural Walls
Structural block walls require steel reinforcement and grout:
When Rebar is Required:
- Walls over 4 feet tall
- Retaining walls of any height
- Seismic zones (Zone 3 and 4)
- Walls supporting structural loads
- Basement/foundation walls
- Per local building code specifications
Vertical Rebar Spacing:
| Wall Type | Rebar Size | Typical Spacing | Notes |
|---|---|---|---|
| Non-structural | None or #4 | 48" OC | Minimal reinforcement |
| Light structural | #4 | 32" OC | Garden walls, short fences |
| Standard structural | #5 | 24" OC | Most residential walls |
| Heavy duty | #5 or #6 | 16" OC | Retaining walls, tall walls |
| High seismic | #6 | 16" OC | Per engineer specifications |
Horizontal Rebar (Bond Beams):
- Required every 4 feet of wall height minimum
- Use bond beam blocks (U-shaped) to create channels
- Typically #4 or #5 rebar continuous
- Lap splices: 40 bar diameters (20" for #4, 25" for #5)
- Install at top of wall and above/below openings
Grout Requirements:
| Fill Type | Grout per 100 8" Blocks | Cost per Block |
|---|---|---|
| Cores with rebar only | 0.5 cubic yards | ~$1.50 |
| All cores filled | 1.0-1.2 cubic yards | ~$3.00 |
| Solid grouted | 1.5+ cubic yards | ~$4.50 |
Grout Specifications:
- Minimum strength: 2,000 PSI at 28 days
- Slump: 8-10 inches for pumpability
- Fine grout for cores under 2" × 3"
- Coarse grout for larger cores
2026 Block and Masonry Material Costs
Current pricing for CMU and related materials:
Standard Block Prices (each):
| Block Size | Standard Gray | Lightweight | Split Face |
|---|---|---|---|
| 4" × 8" × 16" | $1.25-1.75 | $1.50-2.00 | $2.50-3.50 |
| 6" × 8" × 16" | $1.50-2.00 | $1.75-2.50 | $3.00-4.00 |
| 8" × 8" × 16" | $1.75-2.50 | $2.25-3.00 | $3.50-5.00 |
| 10" × 8" × 16" | $2.25-3.00 | $2.75-3.50 | $4.00-6.00 |
| 12" × 8" × 16" | $2.75-3.75 | $3.25-4.25 | $5.00-7.50 |
Specialty Block Prices:
| Block Type | Price Each |
|---|---|
| Half block (8") | $1.50-2.00 |
| Corner block | $2.50-3.50 |
| Bond beam block | $3.00-4.00 |
| Lintel block | $4.00-6.00 |
| Cap block | $2.00-3.00 |
| Split face/scored | $3.50-6.00 |
Other Materials:
| Material | Unit | Price Range |
|---|---|---|
| Mortar mix (60 lb) | bag | $5-8 |
| Mortar mix (80 lb) | bag | $7-11 |
| Portland cement (94 lb) | bag | $12-16 |
| Mason sand | cubic yard | $30-50 |
| #4 rebar | 20' stick | $8-12 |
| #5 rebar | 20' stick | $12-18 |
| Grout (bagged) | 50 lb bag | $8-12 |
| Ready-mix grout | cubic yard | $180-250 |
Labor Costs (Professional):
- Block laying: $8-15 per square foot
- Foundation walls: $12-18 per square foot
- Retaining walls: $15-25 per square foot
- Total installed cost: $15-35 per square foot
Building a CMU Block Wall: Step-by-Step
Proper technique ensures a strong, straight, level wall:
Foundation Requirements:
- Concrete footing minimum 12" wide for 8" block
- Footing width = 2× wall width is typical code requirement
- Footing depth: Below frost line (24-48" depending on region)
- Footing thickness: 8" minimum, typically equals wall width
- Level to within 1/4" over entire length
- Rebar dowels for wall reinforcement if required
Wall Construction Process:
-
Layout and Prep:
- Snap chalk lines on footing for block placement
- Mark rebar locations if required
- Dry-lay first course to check spacing and cuts
-
Corner Leads:
- Build corners first, typically 4-5 courses high
- Use corner poles or transit for plumb
- Check diagonal measurements for square
-
First Course:
- Apply full bed of mortar on footing
- Set corner blocks first
- Run mason's line between corners
- Butter head joints and set blocks
- Check level every 2-3 blocks
-
Building Up:
- Stagger vertical joints (running bond pattern)
- Keep string line at top of each course
- Check plumb and level continuously
- Tool joints when mortar is "thumbprint firm"
-
Finishing:
- Install bond beams at specified heights
- Place and grout rebar
- Install cap blocks or other top treatment
Course Height Reference:
| Courses | Wall Height | Common Use |
|---|---|---|
| 1 | 8" | Raised bed, border |
| 3 | 2' 0" | Low garden wall |
| 6 | 4' 0" | Privacy fence, short retaining |
| 9 | 6' 0" | Tall privacy wall |
| 12 | 8' 0" | Standard wall height |
| 15 | 10' 0" | Commercial/industrial |
Retaining Wall Considerations
Block retaining walls require additional engineering:
Height Limitations:
- DIY limit: 4 feet or less (check local codes)
- Over 4 feet: Engineer-designed typically required
- Over 8 feet: Significant structural engineering needed
Design Requirements:
| Wall Height | Base Width | Rebar | Drainage |
|---|---|---|---|
| 0-2 feet | 8" block | Optional | Gravel behind |
| 2-4 feet | 10" block | #4 @ 32" OC | Drain pipe + gravel |
| 4-6 feet | 12" block | #5 @ 24" OC | Drain + waterproofing |
| 6+ feet | Engineer spec | Per design | Full drainage system |
Drainage System:
- Place filter fabric against soil
- Install 4" perforated drain pipe at base
- Backfill with 12" of washed gravel
- Direct drain to daylight or storm system
- Never backfill with heavy clay soil
Waterproofing:
- Below-grade walls need waterproofing membrane
- Apply to exterior face before backfilling
- Drainage board protects membrane and aids water flow
- Consider dimple board for crawlspace/basement walls
Structural Footing:
- Width: Minimum 2× wall thickness + toe
- Keyway: Groove in footing top for wall placement
- Reinforcement: #4 bars continuous, hooks at ends
- Toe extension: 1/3 of footing extends beyond wall face
Surcharge Considerations:
- Driveways, parking near wall = extra pressure
- Buildings near wall require engineering
- Sloping ground above wall increases load
- Factor these into design before building
Code Requirements and Inspections
Building codes govern masonry construction for safety:
When Permits Are Required:
- Any structural wall
- Walls over 4 feet tall (varies by jurisdiction)
- Retaining walls over 30-48 inches
- Walls attached to buildings
- Foundation walls
Common Code Requirements:
| Requirement | Typical Standard |
|---|---|
| Footing width | 2× wall width minimum |
| Footing depth | Below frost line |
| Minimum block thickness | 6" non-structural, 8" structural |
| Vertical rebar | #4 at 48" OC minimum for structural |
| Horizontal rebar | Every 4' of wall height |
| Grout fill | All cells with rebar, corners, ends |
| Mortar type | Type S below grade, Type N above |
Inspection Points:
- Footing excavation and rebar (before pour)
- Footing after pour (within 24 hours)
- Wall reinforcement in place (before grouting)
- Final wall completion
- Waterproofing (if applicable)
Documentation to Keep:
- Building permit and approved plans
- Inspection sign-offs
- Mortar and grout delivery tickets
- Rebar mill certificates (commercial)
- As-built drawings for complex projects
Common Code Violations:
- Insufficient footing size
- Missing or incorrect rebar placement
- Wrong mortar type for application
- No drainage behind retaining walls
- Building without permit
DIY vs Professional Installation
Evaluate your project scope before deciding:
DIY-Friendly Projects:
- Garden walls under 3 feet
- Raised bed planters
- Outdoor kitchen base
- Small retaining walls (under 2 feet)
- Privacy wall sections
Hire a Professional For:
- Foundation walls
- Structural/load-bearing walls
- Retaining walls over 4 feet
- Walls requiring engineering
- Commercial or code-inspected work
DIY Cost Savings:
| Project Size | Material Cost | Pro Labor | DIY Savings |
|---|---|---|---|
| 100 sq ft | $400-600 | $800-1,200 | $800-1,200 |
| 200 sq ft | $700-1,000 | $1,500-2,400 | $1,500-2,400 |
| 400 sq ft | $1,200-1,800 | $3,000-4,800 | $3,000-4,800 |
Tools Needed for DIY:
- Mason's line and blocks
- 4' level and line level
- Trowel set (brick, pointing, margin)
- Joint striker/jointing tool
- Mixing tub or mixer
- Wheelbarrow
- Work gloves and safety glasses
- Knee pads
Common DIY Mistakes:
- Not checking level frequently enough
- Mortar too wet or too dry
- Working with wet or frozen blocks
- Inadequate footing
- Skipping control joints
- Rushing the job
Pro Tip: Practice on a small project first (mailbox post base, small planter) before tackling a major wall.
Pro Tips
- 💡Order 10% extra blocks for cutting, breakage, and future repairs—matching blocks years later is often impossible.
- 💡Use half blocks at corners and openings rather than cutting—they're stronger and save significant time.
- 💡Stack block pallets on plywood to prevent ground moisture absorption, which weakens blocks.
- 💡In hot weather, dampen blocks lightly to prevent them from sucking moisture from mortar too quickly.
- 💡Never use damaged or cracked blocks—they weaken the wall structure and allow water infiltration.
- 💡Build corner leads first (4-5 courses high), then fill between using a mason's line for alignment.
- 💡Tool mortar joints when they reach "thumbprint firmness"—too early makes them rough, too late prevents proper compression.
- 💡Keep bags of mortar off the ground and under cover—even partial wetting dramatically reduces strength.
- 💡For retaining walls, always install drainage—a 4" perforated pipe with gravel backfill prevents hydrostatic pressure.
- 💡Check level every 2-3 blocks and plumb every course—errors compound quickly in masonry work.
- 💡Install control joints every 20-25 feet to prevent random cracking from expansion and contraction.
- 💡In cold weather, never lay block if temperature is below 40°F or falling—use winter admixtures if necessary.
Frequently Asked Questions
Calculate wall square footage (length × height in feet), then multiply by 1.125 for standard 8×8×16 blocks. A 20-foot long, 8-foot tall wall (160 sq ft) needs approximately 180 blocks. Add 5-10% for breakage and cutting, bringing the total to about 198 blocks. Subtract openings: a standard 3'×7' door removes about 24 blocks.
