Concrete Block Calculator

Estimate concrete masonry units (CMU) for foundation, garden and retaining walls. Nominal block sizes already include the ⅜ in mortar joint.

ft²
%

Blocks needed

149 blocks

  • Blocks per square foot1.125
  • Courses (rows)6
  • Wall area120 ft²

Estimates only. Round up when you order, and confirm structural details with your local building code.

How to use it

  1. Enter the wall length and height.
  2. Subtract openings.
  3. Pick the block face size.

The formula

Blocks per ft² = 144 ÷ (nominal length × nominal height)

Standard 8 × 16 in block = 1.125 per ft²

Worked example

Wall length30 ft
Wall height4 ft
Openings to subtract0 ft²
Block face size (nominal)16 × 8 in (standard CMU)
Waste / spillage allowance10 %

Result

Blocks needed149 blocks
Blocks per square foot1.125
Courses (rows)6
Wall area120 ft²

Tips before you order

  • Lay out the wall in 8 in modules to minimise cut blocks.
  • Corners and openings use special corner and jamb blocks — count them separately when you order.

Questions

How many cinder blocks for a 4 ft wall?

Each foot of wall 4 ft high needs 4.5 standard 8 × 16 blocks — so 135 blocks for a 30 ft wall before waste.