How many concrete blocks do I need per square foot?

For standard 8×8×16 CMU blocks with 3/8-inch mortar joints: 1.125 blocks per square foot. Multiply net wall area (excluding openings) by 1.125, then add 5–10% for waste. For a 300 sq ft wall, that's approximately 338–360 blocks.

What size concrete block is most common?

The 8×8×16 nominal CMU (actual size 7-5/8 × 7-5/8 × 15-5/8 inches) is the most common size for residential and light commercial construction. The nominal size includes the 3/8-inch mortar joint.

How much mortar do I need for concrete blocks?

Approximately 3 bags of 60-lb Type S or Type N mortar per 100 standard 8×8×16 blocks. For a 360-block project, you'd need 10–11 bags of pre-mixed mortar, plus water. Type S is required for below-grade and load-bearing applications.

Do I need to fill concrete blocks with concrete?

Building code requirements vary. For load-bearing walls, most codes require vertical rebar and grout-filled cores at specified intervals (commonly every 24–48 inches). Fully grouted walls are required in seismic zones and for walls over a certain height. Check local building codes and consult a structural engineer for any load-bearing application.

How many concrete blocks are on a pallet?

Standard 8×8×16 CMU blocks are typically delivered on pallets of 75–90 blocks. Calculate your total block count and round up to the nearest full pallet quantity to minimize delivery costs.

Concrete Block Calculator: How Many CMU Blocks Do You Need?

Calculate the number of concrete masonry units (CMU) for any wall project. Covers standard block sizes, mortar joints, waste factors, and typical weights and costs.

Related Calculators

Asphalt Calculator
Calculate asphalt tonnage needed for a driveway or paving project.
Baseboard Calculator
Estimate baseboard linear footage, stock pieces and material cost from room perimeter, excluded openings, waste and board length.
CMU Block Calculator
Estimate how many standard 8x8x16 concrete masonry units (CMU) you need for a wall.
Concrete Block Calculator
Estimate the number of concrete blocks needed for a rectangular wall, including a waste allowance.
Concrete Driveway Cost Calculator
Estimate the cost of pouring a concrete driveway.
Fence Post Depth Calculator
Estimate fence post hole depth from post height, frost depth and gravel base.

Standard Concrete Block Sizes

Concrete Masonry Units (CMU) are manufactured to standard nominal dimensions. The actual size is 3/8 inch smaller in each direction to account for a standard 3/8-inch mortar joint:

Nominal Size	Actual Size (L × H × W)	Common Use
16×8×8 inches	15-5/8 × 7-5/8 × 7-5/8 in	Foundation walls, retaining walls
16×8×4 inches	15-5/8 × 7-5/8 × 3-5/8 in	Non-load-bearing partitions
16×8×12 inches	15-5/8 × 7-5/8 × 11-5/8 in	Heavy-load walls

The most common is the 8×8×16 CMU — used for most residential and light commercial applications.

How to Calculate Block Count

Step 1: Calculate wall area Wall Area (sq ft) = Wall Width (ft) × Wall Height (ft)

Subtract openings (doors, windows) from the total.

Step 2: Blocks per square foot For 8×8×16 nominal blocks with 3/8-inch mortar joints: - Each block + joint covers: 16 in × 8 in = 128 sq in = 0.889 sq ft - Blocks per sq ft: 1 ÷ 0.889 = 1.125 blocks per square foot

Step 3: Add waste factor - New construction: 5% waste - Cuts around openings, curves: 7–10% waste

Step 4: Total blocks needed Total = Wall Area × 1.125 × (1 + Waste Factor)

Worked Example

A 40 ft long × 8 ft tall foundation wall with a 3 ft × 7 ft door opening:

Gross wall area: 40 × 8 = 320 sq ft
Door opening: 3 × 7 = 21 sq ft
Net wall area: 320 − 21 = 299 sq ft
Blocks needed (net): 299 × 1.125 = 336 blocks
With 7% waste: 336 × 1.07 = 360 blocks

Always round up to the nearest full pallet. Blocks are typically sold in quantities of 75–90 per pallet.

Mortar Requirements

For each 100 standard 8×8×16 blocks, you need approximately: - 3 bags of Type S mortar (60-lb bags) for standard 3/8-inch bed and head joints - Or 2.5 to 3 cubic feet of masonry mortar mix

Type S mortar (minimum 1,800 psi compressive strength) is standard for below-grade and load-bearing applications. Type N (750 psi) is acceptable for above-grade non-load-bearing walls.

Block Weights and Structural Notes

Fill Condition	Weight per 8×8×16 Block
Hollow (unfilled)	28–36 lbs
Partially grouted	40–50 lbs
Fully grouted	55–65 lbs

Building codes (IBC) require vertical and horizontal reinforcement in most CMU structures. Typical residential foundation walls use #5 rebar vertically every 24–32 inches and horizontal joint reinforcement (ladder or truss type) every other course. Always consult local building codes and a structural engineer for load-bearing walls.

Cost Estimate

Item	Typical Unit Cost	Cost for 360 Blocks
8×8×16 CMU blocks	$1.50–$3.00 each	$540–$1,080
Mortar (60-lb bags)	$8–$12/bag	$90–$130 (11 bags)
Rebar (#5, 20-ft)	$12–$18/bar	Varies by design
Labor (mason)	$60–$120/hr	—

Material costs for a 360-block project: approximately $700–$1,300 without labor.

Frequently Asked Questions

How many concrete blocks do I need per square foot?: For standard 8×8×16 CMU blocks with 3/8-inch mortar joints: 1.125 blocks per square foot. Multiply net wall area (excluding openings) by 1.125, then add 5–10% for waste. For a 300 sq ft wall, that's approximately 338–360 blocks.
What size concrete block is most common?: The 8×8×16 nominal CMU (actual size 7-5/8 × 7-5/8 × 15-5/8 inches) is the most common size for residential and light commercial construction. The nominal size includes the 3/8-inch mortar joint.
How much mortar do I need for concrete blocks?: Approximately 3 bags of 60-lb Type S or Type N mortar per 100 standard 8×8×16 blocks. For a 360-block project, you'd need 10–11 bags of pre-mixed mortar, plus water. Type S is required for below-grade and load-bearing applications.
Do I need to fill concrete blocks with concrete?: Building code requirements vary. For load-bearing walls, most codes require vertical rebar and grout-filled cores at specified intervals (commonly every 24–48 inches). Fully grouted walls are required in seismic zones and for walls over a certain height. Check local building codes and consult a structural engineer for any load-bearing application.
How many concrete blocks are on a pallet?: Standard 8×8×16 CMU blocks are typically delivered on pallets of 75–90 blocks. Calculate your total block count and round up to the nearest full pallet quantity to minimize delivery costs.

Last updated 7/28/2026