Block Wall Calculator

Enter your wall size and block size to get the number of concrete blocks you need, with the mortar joint and waste built in.

How to use this calculator ↓

What your result means

Blocks is your order count with the 3/8 inch mortar joint and 5% waste built in. Add corner blocks at corners and a grouted bond beam at the top of a structural wall, and run rebar in the cores per your local code. Mortar is roughly one bag per 30 blocks.

How to use this calculator

  1. Measure wall length and height in feet.
  2. Standard CMU is 16 x 8 inches face.
  3. Use 5% waste.
  4. Read total blocks needed.
  5. Order rebar and concrete grout separately if structural.

The formula

wallSqIn = length * height * 144 blockSqIn = (blockL + 0.375) * (blockH + 0.375) // 3/8 in joint blocks = ceil((wallSqIn / blockSqIn) * (1 + waste/100))

Wall area in square inches is length times height times 144. Add 0.375 to the block's length and height for the mortar joint, multiply for one block's footprint, divide, add waste, and round up.

Worked example

Say you've got a 40 ft long, 8 ft tall wall in 16 by 8 inch block with 5% waste. The wall is 320 sq ft, or 46,080 sq inches; each block with its joint covers about 137. That's 336 base blocks and 353 with waste.

Block wall quick reference

ItemValue
Standard CMU face16 x 8 in
Blocks per sq ft~1.125
Wall thickness7 5/8 in (nominal 8)
Mortar1 bag per ~30 blocks

Tips & gotchas

  • Standard CMU face is 16 by 8 inches.
  • The 3/8 inch mortar joint is standard and already in the count.
  • Run rebar in the vertical cores, grouted solid, for a structural wall.
  • Add a bond beam, a grouted horizontal course, at the top of a structural wall.
  • Use corner blocks at the corners so the courses bond properly.

Frequently asked questions

How is a block wall different from a brick wall?

CMU blocks are bigger, hollow, and faster to lay. Brick is solid and more decorative.

Do block walls need rebar?

Yes for any load-bearing or tall wall. Your local code sets the spacing.

How fast can a block wall go up?

An experienced mason lays 100 to 200 blocks a day. DIY is a lot slower.

Can block walls be left unpainted?

Yes, but they look raw. Most people paint them or apply stucco.

How thick are block walls?

Standard CMU is 7 5/8 inches thick, nominally 8 inches.

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Maintained by the CalcWright Team. Formulas verified against industry-standard sources. Last updated: May 25, 2026

Estimates only — see our full disclaimer.