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Cinder Block Calculator

Concrete masonry units

CMU Calculator

Count concrete masonry units with modular 8×16 in faces. CMU is the standard name for what many people still call cinder block.

Calculator

1

Wall dimensions

Enter length and height. Add more sections for corners or extra walls.

ft
ft

No wall sections calculated yet

2

Block size

Nominal face size includes the mortar joint. Width is the wall thickness.

Face dimensions are the wall face (length × height). Width is how deep the block sits in the wall.

3

Doors & windows

Subtract doors and windows from the wall area for a more accurate block estimate.

No openings yet. Solid walls skip this step.

4

Waste allowance

Extra blocks for cuts, breakage, and layout. Actual waste varies by project — this is an estimate, not a requirement.

5

Mortar & core fill

Optional material estimates. Assumptions are listed with the results.

Mortar

in

Default assumes about 33 standard 8×8×16 in blocks per 80 lb bag with a 3/8 in face-shell joint.

Not every wall has grouted cores. This is a volume estimate only — it does not determine reinforcement or engineering requirements.

6

Cost estimate

Optional. Enter your local prices — this tool does not assume market rates.

Enter your wall dimensions to see your estimate.

The diagram updates as you type.

Your estimate will appear here

Add a wall length and height to calculate blocks, mortar, and optional cost.

What CMU means

CMU stands for concrete masonry unit. ASTM C90 (opens in a new tab) is the standard specification for loadbearing concrete masonry units. In the field, CMU, concrete block, and cinder block are often used interchangeably even though true cinder aggregate is uncommon in new production.

Modular layout

CMU walls are designed on an 8 in module. Nominal 8 in height and 16 in length include the mortar joint. That is why this calculator defaults to 8×8×16 in and treats those dimensions as the face coverage per unit.

Width is the wall thickness

4, 6, 8, 10, and 12 in CMU share the same face for counting, but width changes grout volume and structural capacity. Pick the width specified on the drawings. This tool estimates quantity; it does not check whether a width is adequate.

Looking for the full estimator with wall diagram and openings? Use the cinder block calculator.