BLOCK CALCULATOR

Concrete Block Calculator — How Many CMU Blocks Do I Need?

Estimate how many concrete masonry units (CMU) you need for a foundation wall, retaining wall, garden wall or any block masonry project. Choose the block size, enter your wall dimensions and the calculator returns a block count and approximate mortar requirement.

Wall dimensions

Block type

Waste allowance

Blocks needed
—blocks

Enter wall dimensions to calculate.

How Many Concrete Blocks Do I Need?

The standard calculation divides wall area by the face area of a single block including its mortar joint:

Blocks = Wall Area ÷ Block Face Area (inc. mortar joint)

A standard 16×8 in CMU with a 3/8-inch mortar joint covers approximately 0.89 sq ft per block, giving roughly 1.12 blocks per square foot. For most straight walls a 5% waste allowance is sufficient; increase to 10% for walls with many openings or cuts.

Always measure openings such as doors and windows and subtract their area before calculating your block order.

CMU Block Sizes & Applications

  • Standard 8 in CMU (16×8×8 in): ~1.12 blocks/sq ft — general walls
  • Half block (8×8×8 in): corners, openings, course adjustment
  • 4 in solid block (16×4×8 in): partition and veneer walls
  • 6 in CMU (16×6×8 in): lighter retaining walls and partitions
  • Split-face block: decorative exterior walls

Hollow CMU blocks are used for most structural applications and allow rebar and grout to be placed in the cores for reinforced masonry walls.

Mortar & Grout Estimates for Block Walls

In addition to blocks, a CMU wall requires mortar for the bed and head joints and, if reinforced, grout for the cores.

  • Approximately 1 bag of mortar mix per 3–4 standard CMU blocks
  • Core fill grout: roughly 0.045 cu ft per block for 8×8×16 hollow CMU
  • Rebar is typically placed vertically at 32–48 in on center in reinforced walls

Use our Mortar Calculator and Rebar Calculator alongside this tool for a complete materials list.

Frequently Asked Questions

How many CMU blocks are in a standard pallet?

A standard pallet holds approximately 72–90 standard 8×8×16 blocks, though pallet quantities vary by supplier.

What is the weight of a standard CMU block?

A standard 8×8×16 hollow CMU weighs approximately 28–36 lbs depending on aggregate type. Lightweight CMU blocks use expanded shale and weigh around 22–28 lbs.

Do I need permits to build a block wall?

Most jurisdictions require permits for block walls over a certain height (typically 3–4 ft) or retaining walls. Check your local building department before starting.

Brick CalculatorMortar CalculatorRebar CalculatorRetaining Wall Calculator