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Generator Hut

Concrete Block Calculator

Blocks, courses and mortar for a block wall.

Your measurements

A standard 8×8×16 in block covers about 0.89 sq ft of wall face.

Covers breakage and cuts at corners and openings.

Blocks required

284blocks

284 blocks for 240 sq ft

Wall area30 ft × 8 ft
240 sq ft
Courses highat 8 in per course including the joint
12
With waste allowance
+5%
Blocks required
284
Mortar mixabout one 70 lb bag per 28 blocks
≈ 11 bags

Block waste runs lower than brick because the units are larger and fewer cuts are needed per square foot — 5% is usually adequate on a straight run.

Reinforcement, grout fill and bond beams are not included and are frequently required, particularly for retaining walls and anything carrying load. Those are engineering decisions.

Half blocks at corners and openings are a separate item at most suppliers. Count your corners and order them rather than cutting full blocks on site.

Enter the wall dimensions and it returns the block count, the number of courses and an estimate of mortar mix. A standard 8x8x16 inch block presents a face of about 0.89 square feet including its joint, which works out at 1.125 blocks per square foot.

Why use this tool?

Courses counted

How many courses high the wall runs at 8 inches per course including the joint — useful for checking the height works out even.

Mortar estimated

About one 70 lb bag per 28 blocks laid, which is a very different ratio from brickwork.

Lower waste than brick

Larger units mean fewer cuts per square foot, so 5% is usually adequate on a straight run.

Reinforcement flagged

Grout fill, vertical steel and bond beams are frequently required and are engineering decisions, not arithmetic.

How this concrete block calculator works

Wall area times the blocks-per-square-foot figure, plus waste. The default of 1.125 comes from a standard 8 by 16 inch block face, which with its mortar joint covers about 0.89 square feet — and 1 divided by 0.89 is 1.125.

Courses are the wall height in inches divided by 8, since a block plus its bed joint occupies 8 inches of height. Checking that this comes out close to a whole number is worth doing before you start, because a part course at the top is awkward.

Mortar for blockwork runs around one 70 lb bag per 28 blocks — far fewer blocks per bag than bricks, because each block has much more joint length around it despite being a larger unit.

How to use it

  1. Step 1: Measure the wall

    Length and height of the wall face.

  2. Step 2: Check the course count

    If the height does not divide evenly by 8 inches, adjust the wall height or plan for a cut course.

  3. Step 3: Set the waste allowance

    Five per cent is usually enough for a straight run. More for a wall with corners, openings or curves.

  4. Step 4: Order corner blocks separately

    Half blocks and corner units are separate items at most suppliers. Count your corners and order them rather than cutting full blocks.

Example usage

A 30 by 8 wall
240 square feet at 1.125 blocks per square foot, plus 5% waste, is 284 blocks across 12 courses, needing about 11 bags of mortar mix.
A retaining wall
The same block count, but retaining walls need vertical reinforcement, grout fill and often a drainage layer behind. Those are design requirements, not options.
A garage foundation course
A 40 by 4 foot stem wall is 160 square feet, or 189 blocks over 6 courses. Foundation work usually needs rebar and grout in the cells.

Frequently asked questions

How many concrete blocks per square foot?

About 1.125 for a standard 8x8x16 inch block, whose face plus mortar joint covers roughly 0.89 square feet. Divide your wall area by 0.89, or multiply by 1.125.

How much mortar for a block wall?

Roughly one 70 lb bag of mortar mix per 28 blocks. That is far fewer units per bag than brickwork, because each block has more joint length around it.

How many courses will my wall be?

Wall height in inches divided by 8, since each block plus its bed joint occupies 8 inches. An 8 foot wall is 12 courses exactly, which is why 8 foot heights are convenient.

Do block walls need reinforcement?

Frequently, and always for retaining walls or anything carrying load. Vertical steel, grouted cells and bond beams are common requirements, and they are engineering decisions rather than rules of thumb.

Why is block waste lower than brick waste?

Larger units mean fewer of them per square foot and fewer cuts at the perimeter. A straight block run often needs only 5 per cent where brickwork needs 10.

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