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Concrete & Masonry

Concrete Block Calculator

Use this concrete block calculator to count CMU blocks and courses for a wall; our masonry repair guide covers block walls and foundations. Standard concrete masonry units (CMU) have a nominal face of 16 × 8 in — the actual block is 3/8 in smaller to leave room for the mortar joint — so every block covers 0.889 sq ft of wall, or 1.125 blocks per square foot, regardless of whether it is 4, 6, 8 or 12 inches thick.

Results from this concrete block calculator are planning estimates; confirm quantities and prices with your supplier or contractor before you order.

Enter your project

ft
in
m
ft
in
m
sq ft
m²
%

Extra for cuts, breakage and spillage.

From your mortar bag label or mason.

Results

Your results will appear here

Enter your measurements and press Calculate. Defaults show a typical example.

How to use the concrete block calculator

  1. Enter wall length and height; subtract door and window openings.
  2. Choose the block face size.
  3. Add waste for cuts and breakage.
  4. Optionally enter how many blocks one bag of mortar lays.

Formula

Blocks = (L × H − openings) ÷ face area × (1 + waste). For 16 × 8 nominal blocks the face area is 0.889 sq ft, i.e. 1.125 blocks per sq ft.

Worked example

A 20 × 8 ft wall is 160 sq ft × 1.125 = 180 blocks; with 5% waste, 189 blocks in 12 courses.

Tips for using the concrete block calculator

  • Plan wall lengths in 8 in increments where you can, so blocks fit without cutting.
  • Order corner and half blocks separately; they are counted as full blocks here.
  • Foundation and retaining walls usually need rebar and grouted cores; check your plans or code first.
Mason laying concrete blocks beside stacked block pallets on a site

Concrete Block Calculator FAQs

How many cinder blocks per square foot?

1.125 standard 8 × 16 in (nominal) blocks per square foot.

Do I need to fill the cores?

Cores are grouted and reinforced where the design calls for it — commonly at rebar locations, or fully for retaining and foundation walls. Grout quantities depend on the block and design; ask your supplier or engineer.

Are foundation walls a DIY job?

Foundation and retaining walls carry soil loads and usually need permits and design. See our foundation guide.

Estimate before you call a contractor

Run the numbers with our free calculators so you can compare bids with confidence.

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