How many blocks are in a square foot of wall?

1.125 for standard 8 × 8 × 16 block. The face is 8 inches by 16 with a 3/8 inch mortar joint on two sides, which works out to 8/9 of a square foot per block — so nine blocks cover eight square feet. Half-height block doubles the count and 12-inch block does not change it, because only the width differs.

What is the difference between a cinder block and a concrete block?

Cinder block was made with coal cinders as the aggregate and is largely historical; what is sold today is concrete masonry unit — CMU — made with sand and gravel. The names are used interchangeably in conversation and only the modern product is actually available, so a "cinder block" quote is a CMU quote.

Do I need to fill the cores?

Only where the design calls for it. Filled cores with rebar make a structural wall that resists lateral load, which a retaining wall or a tall freestanding wall needs; a garden wall usually does not. Filling every core on a 320 square foot wall takes about five cubic yards of concrete, so it is not a small decision.

How much mortar does a block wall take?

Around three 70 lb bags of mortar mix per hundred blocks for a standard 3/8 inch joint, and a little more for a first course laid on an uneven footing. Buy at least one extra bag: running out mid-course means a cold joint where the new mortar will not bond to the old.

Concrete Block Calculator

With wall length 40 ft, wall height 8 ft, openings to deduct 0 sq ft, waste allowance 5 percent and 1 more field, concrete block comes to 378 blocks — blocks to order. It is reached in 7 steps, the last of which is ceil(320 * 1.125 * (1 + 5 / 100)), and each one is printed on the page with its numbers filled in. The formula is the one published by NIST Handbook 44, Appendix C, not an approximation fitted to it.

Blocks, mortar and fill for a concrete block wall, from its length and height. Blocks, courses, mortar and the concrete it takes to fill the cores.

Formula and sources checked 27 August 2026 · How we check

Wall length 40 ft, Wall height 8 ft, Block size 8 × 8 × 16 in (standard CMU), Waste allowance 5

378 blocks

Blocks to order for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.

It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.

Wall lengthWall heightBlock sizeOpenings to deductsq ftWaste allowancepercentFill the coresGrout poured into the block cavities, with rebar, for a structural wall.Price per blockusd

Blocks to order

378 blocks

Wall area: max(0, 40 * 8 - 0)320 sq ft
Blocks per square foot: 1.125
Blocks needed: ceil(320 * 1.125 * (1 + 5 / 100))378 blocks
Courses high: ceil(8 * 12 / (8))12
Mortar bags (70 lb): ceil(378 / 100 * 3)12 bags
Concrete to fill the cores: 0 cu yd
Block cost: 378 * 2.4$907.20

Several at once

A job is rarely one of anything. Work out the first, add it, change the figures and add the next — the list keeps what each line was, and totals them.

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Worked example

A 40 ft wall 8 ft high is 320 square feet. Standard blocks lay 1.125 to the square foot including the mortar joint, so 360 blocks plus 5% waste is 378 — and 12 courses high, since a block with its joint is 8 inches.

How to work it out yourself

1.Measure the wall face, then deduct any door or window openings in square feet.
2.Count 1.125 blocks per square foot for standard 8 × 8 × 16 block. The figure already includes the mortar joint, which is why it is not 1.
3.Order mortar at about three 70 lb bags per hundred blocks, and sand at about a cubic yard per 25 bags if you are mixing rather than buying premixed.

The formula

Wall areamax(0, 40 * 8 - 0)
Blocks per square foot
Blocks neededceil(320 * 1.125 * (1 + 5 / 100))
Courses highceil(8 * 12 / (8))
Mortar bags (70 lb)ceil(378 / 100 * 3)
Concrete to fill the cores
Block cost378 * 2.4

Source: NIST Handbook 44, Appendix C — general tables of units of measurement

Questions people actually ask

How many blocks are in a square foot of wall?: 1.125 for standard 8 × 8 × 16 block. The face is 8 inches by 16 with a 3/8 inch mortar joint on two sides, which works out to 8/9 of a square foot per block — so nine blocks cover eight square feet. Half-height block doubles the count and 12-inch block does not change it, because only the width differs.
What is the difference between a cinder block and a concrete block?: Cinder block was made with coal cinders as the aggregate and is largely historical; what is sold today is concrete masonry unit — CMU — made with sand and gravel. The names are used interchangeably in conversation and only the modern product is actually available, so a "cinder block" quote is a CMU quote.
Do I need to fill the cores?: Only where the design calls for it. Filled cores with rebar make a structural wall that resists lateral load, which a retaining wall or a tall freestanding wall needs; a garden wall usually does not. Filling every core on a 320 square foot wall takes about five cubic yards of concrete, so it is not a small decision.
How much mortar does a block wall take?: Around three 70 lb bags of mortar mix per hundred blocks for a standard 3/8 inch joint, and a little more for a first course laid on an uneven footing. Buy at least one extra bag: running out mid-course means a cold joint where the new mortar will not bond to the old.

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