Concrete Block Estimator: Blocks per Square Foot
Blocks = wall area in square feet × blocks per square foot, plus waste, rounded up. Block sizes are quoted nominal, which means the 3/8 inch mortar joint is included: a block sold as 8 by 8 by 16 inches measures 7 5/8 by 7 5/8 by 15 5/8 inches, and it occupies 8 by 16 inches of wall. That face covers 128 square inches, so 144 ÷ 128 gives 1.125 blocks per square foot. The Titan America estimating guide lists the same 1.125 for standard blocks 4, 8, 10 and 12 inches thick, and 2.25 for the half-high block.
| Block face (height × length) | Sq ft per block | Blocks per sq ft | Per 100 sq ft, no waste | Per 100 sq ft, 5% waste |
|---|---|---|---|---|
| Standard, 8 x 16 in face | 0.889 | 1.125 | 113 | 119 |
| Half-high, 4 x 16 in face | 0.444 | 2.250 | 225 | 237 |
For the standard block, CMHA/NCMA TEK 04-02A, Estimating Concrete Masonry Materials, says that with a 5 percent allowance for waste and breakage you need 119 units per 100 square feet of wall, which matches the last column. For any other nominal size choose Custom face size in the calculator.
Block Wall Calculator: How Many Concrete Blocks Do I Need?
- Find the wall area. Multiply the length by the height in feet. Measure the height to the top of the last block course.
- Take out openings. Multiply the width by the height of each door or window and subtract the total. A 3 by 7 ft door is 21 square feet, which is about 24 blocks off the count. TEK 04-02A says to subtract openings from the wall area and to count pilaster, corner and bond beam units separately.
- Multiply by 1.125. That is the count for a standard block with no waste.
- Add waste and round up. The default is 5 percent, from TEK 04-02A. Raise it for a wall with many corners or cuts.
The calculator does all four steps, and it also shows the number of courses and the blocks in each course so you can check the count against a sketch of the wall.
Block Count Chart
This chart shows blocks to buy, including 5 percent waste, for standard 8 by 16 inch blocks and common wall sizes with no openings.
| Wall length | 2 ft high | 3 ft high | 4 ft high | 5 ft high | 6 ft high |
|---|---|---|---|---|---|
| 8 ft | 19 | 29 | 38 | 48 | 57 |
| 12 ft | 29 | 43 | 57 | 71 | 86 |
| 16 ft | 38 | 57 | 76 | 95 | 114 |
| 20 ft | 48 | 71 | 95 | 119 | 142 |
| 24 ft | 57 | 86 | 114 | 142 | 171 |
| 32 ft | 76 | 114 | 152 | 189 | 227 |
Block Wall Mortar
Mortar is bought by the bag, and the number of blocks a bag lays depends on what is in the bag. The calculator offers three common choices and divides the blocks you are buying by the blocks one bag lays, rounding up. The yields assume face shell bedding, where mortar goes on the long edges of the block and not across the webs.
| Mortar | Blocks one bag lays | Source |
|---|---|---|
| Pre-blended mortar mix, 80 lb (add water) | up to 13 | QUIKRETE Mortar Mix (Type N) and Mason Mix (Type S) data sheets |
| Masonry cement, 70 lb, mixed with sand | about 30 | CMHA/NCMA TEK 04-02A |
| Portland cement, 94 lb, mixed with lime and sand | about 62 | CMHA/NCMA TEK 04-02A |
The bags are not the same product, so the counts do not compare bag for bag: a pre-blended bag already contains sand, while masonry cement and portland cement are mixed with sand you buy separately. TEK 04-02A puts the sand for masonry cement mortar at about 240 blocks per ton, and the calculator shows the tons when you choose it. QUIKRETE words its figure as “up to”, so treat the pre-blended count as the most you should expect from a bag. Titan America’s guide gives 3 bags per 100 blocks without naming a bag size, which falls between the pre-blended and the masonry cement numbers.
| Blocks to buy | Pre-blended, 80 lb bags | Masonry cement, 70 lb bags | Sand with masonry cement | Portland cement, 94 lb bags |
|---|---|---|---|---|
| 50 | 4 | 2 | 0.21 tons | 1 |
| 100 | 8 | 4 | 0.42 tons | 2 |
| 200 | 16 | 7 | 0.83 tons | 4 |
| 500 | 39 | 17 | 2.08 tons | 9 |
Need sand for a different job, such as bedding under pavers or a play area? The Sand Calculator sizes that from an area and depth, and the sand for the mortar above is already in the tons column.
Concrete Block Fill Calculator: Filling the Cores
Some walls have grout or concrete poured into the hollow cores, often around reinforcing bar. Titan America’s estimating guide lists the approximate volume to fill the cores of a two-core block that is 8 inches high and 16 inches long, by thickness. It gives no figure for 4 inch blocks or for other face sizes, so the calculator offers core fill only for the standard face in 6, 8, 10 and 12 inch thickness. A two-core 16 inch unit has a core every 8 inches, so filling every other core is half the cores and every fourth core, 32 inches apart, is a quarter; which cores to fill comes from your plans.
| Block thickness | Cu ft to fill one block | Cu ft per 100 blocks | Cu ft per 100 sq ft of wall | Cu yd per 100 sq ft of wall |
|---|---|---|---|---|
| 6 in | 0.17 | 17 | 19.2 | 0.71 |
| 8 in | 0.25 | 25 | 28.3 | 1.05 |
| 10 in | 0.33 | 33 | 37.3 | 1.38 |
| 12 in | 0.39 | 39 | 44.1 | 1.63 |
The last two columns multiply the per-block figure by the 112.5 blocks in 100 square feet with every core filled. The fill is figured on the blocks in the wall, not the waste, and it does not include extra for spillage or a bond beam, which Titan America lists separately. The Cubic Yard Calculator converts the volume to a delivery weight.
Courses and Cap Units
A standard block is 8 inches high including the joint, so each course adds 8 inches. A wall height that is not a multiple of 8 rounds up to the next whole course, so measure to the top of the last course you will lay.
| Courses | Wall height |
|---|---|
| 3 | 24 in (2 ft) |
| 4 | 32 in (2.67 ft) |
| 5 | 40 in (3.33 ft) |
| 6 | 48 in (4 ft) |
| 8 | 64 in (5.33 ft) |
| 9 | 72 in (6 ft) |
| 12 | 96 in (8 ft) |
A cap course is a row of solid or cap units on the top of the wall. The calculator counts one cap per 16 inches of wall length by default, the modular length of a standard unit, and you can change the length to match the caps your supplier sells. The cap course sits on top of the wall height you entered, so it is counted separately from the blocks.
| Wall length | Cap units, 16 in each | With 5% waste |
|---|---|---|
| 8 ft | 6 | 7 |
| 12 ft | 9 | 10 |
| 20 ft | 15 | 16 |
| 32 ft | 24 | 26 |
| 50 ft | 38 | 40 |
Concrete Block Wall Cost
The calculator turns the quantities on this page into a cost when you type in prices. Open Optional under the results and enter the price per block, the price of a mortar bag, the price per cap unit and the price of core fill per cubic yard. Nothing is pre-filled, because block prices change with region, color, finish and delivery, and a blank price adds nothing. For the 20 by 4 ft example below, each line multiplies like this.
| Line | Quantity in the example | Multiply by |
|---|---|---|
| Blocks | 95 blocks | Your price per block |
| Mortar | 8 pre-blended bags, or 4 masonry cement bags plus 0.40 tons of sand | Your price per bag (and per ton of sand) |
| Cap units | 16 units | Your price per cap |
| Core fill | 0.83 cubic yards, every core | Your price per cubic yard |
Delivery, the footing, reinforcing steel, flashing, sealer and tool rental are not included, so add them from your quotes. Block weight is not a standard figure, so check the weight per pallet with your supplier before the delivery arrives.
Worked Example
Say you are building a 20 × 4 ft garden wall in standard 8 × 8 × 16 inch blocks with a cap course.
- Area: 20 × 4 = 80 sq ft, with no openings.
- Blocks: 80 × 1.125 = 90, or 95 with 5 percent waste.
- Courses: 48 ÷ 8 = 6 courses with 15 blocks in each (240 ÷ 16).
- Mortar: 95 blocks need 8 pre-blended 80 lb bags, or 4 bags of 70 lb masonry cement with about 0.40 tons of sand, or 2 bags of 94 lb portland cement.
- Cap units: 240 ÷ 16 = 15, or 16 with 5 percent waste.
- Core fill (8 inch blocks, if you fill them): 90 × 0.25 = 22.5 cu ft, which is 0.83 cubic yards with every core filled and 11.3 cu ft with every other core.
For a gravel base under the first course, the Gravel Calculator gives cubic yards and tons, and for a patio beside the wall the Paver Calculator counts the pavers.
When You Need an Engineer
This calculator counts materials for garden walls, planters and the foundations of small structures. It does not design a wall. Retaining walls, load-bearing walls and walls that carry a roof or a floor are engineered, and their reinforcement, grout spacing, footing size and maximum height come from your local building code and the plans. Ask your building department whether a permit is needed before you buy blocks, and use the quantities here to price the job once the design is settled.
Common Mistakes
- Using actual block dimensions. A block that measures 7 5/8 by 15 5/8 inches is laid on an 8 by 16 inch module, because the joint is part of the nominal size. Counting by the actual size overstates the blocks.
- Forgetting the openings. Subtract each door and window from the wall area, as TEK 04-02A says, and then count the lintels, corners and bond beam units separately.
- Skipping the waste allowance. TEK 04-02A includes 5 percent for waste and breakage. An exact count leaves no spare blocks for cuts or breakage.
- Treating mortar bags as interchangeable. A pre-blended 80 lb bag lays up to 13 blocks and a 70 lb bag of masonry cement about 30, because the cement bag is mixed with sand you buy separately. Check which product the price is for.
- Counting the cap course as wall height. Cap units sit on top and are bought separately, so they are not in the block count.
- Pricing only the blocks. Mortar, sand, caps, fill, the footing, reinforcing steel and delivery are separate lines, which is why the cost section above prices each one.
- Assuming core fill is the same for every block. The volume depends on the block thickness and the face, and the source figures cover the standard face in 6 to 12 inch thickness only.
Concrete Block Calculator FAQ
How many concrete blocks do I need per square foot?
A standard block with a nominal 8 by 16 inch face takes 1.125 per square foot, or 112.5 per 100 square feet, because the nominal size includes the 3/8 inch mortar joint and 144 square inches divided by 128 is 1.125. The Titan America estimating guide gives the same figure for 4, 8, 10 and 12 inch thick blocks, since thickness does not change the face. CMHA/NCMA TEK 04-02A adds a 5 percent allowance for waste and breakage and lands on 119 blocks per 100 square feet.
How many blocks does a 20 foot long, 4 foot high wall take?
That wall is 80 square feet, which is 90 blocks of the standard size and 95 with 5 percent waste. It is 6 courses high with 15 blocks in each course. Change the length, height or openings in the calculator and it recounts.
Can I use this as a cinder block or CMU calculator?
Yes. Cinder block is everyday shorthand for the concrete masonry unit (CMU), and the standard unit is the same 8 by 8 by 16 inch nominal block, so the counts are the same: a 20 by 4 ft wall takes 95 cinder blocks with 5 percent waste. If your units have an unusual face size, such as old or specialty blocks, choose Custom face size and enter the nominal height and length, which count the mortar joint.
How much mortar do I need for 100 blocks?
It depends on the mortar you buy, because bag yields differ. For 100 blocks that is about 8 bags of pre-blended 80 lb mix (up to 13 blocks per bag, QUIKRETE), 4 bags of 70 lb masonry cement mixed with sand (about 30 blocks per bag, NCMA) or 2 bags of 94 lb portland cement mixed with lime and sand (about 62 blocks per bag, NCMA). Titan America puts it at 3 bags per 100 blocks without naming a bag size. The table above shows more block counts.
How many concrete blocks do I need for 1,000 square feet of wall?
A 1,000 square foot wall takes 1,125 standard blocks with no waste and 1,182 with a 5 percent allowance (1,000 × 1.125, then 5 percent more, rounded up). Subtract the area of every door and window first, then count corner, pilaster and bond beam units separately, as TEK 04-02A says.
How much block fill do I need per 100 blocks?
Titan America lists about 0.25 cubic feet to fill every core of an 8 inch thick standard block, so 100 blocks take about 25 cubic feet, or 0.93 cubic yards. For 6, 10 and 12 inch thick blocks it is 17, 33 and 39 cubic feet. That is for every core; filling every other core is half.
How many blocks will 1 cubic yard of concrete fill?
A cubic yard is 27 cubic feet. At 0.25 cubic feet per 8 inch thick block with every core filled, that is 27 ÷ 0.25 = 108 blocks, which is about 96 square feet of wall. For 6, 10 and 12 inch thick blocks the same yard fills about 158, 81 and 69 blocks. Spillage and any bond beam are extra.
How much extra should I order for cuts and breakage?
CMHA/NCMA TEK 04-02A includes a 5 percent allowance for waste and breakage, which is the calculator default. Corners, the top course and any cut around an opening use more, so raise it for a wall with many corners or openings. Pilasters, corner units and bond beam units are counted separately in the TEK, so list those on top.
Do I have to fill the cores of concrete blocks?
Not by default. Whether cores are filled, which ones and with what comes from the design and your local code, not from this tool. When you do fill them, the calculator gives the volume: Titan America lists about 0.25 cubic feet to fill every core of an 8 inch thick block, and the options are every core, every other core or every fourth core. For the 20 by 4 ft wall that is 22.5 cubic feet (0.83 cubic yards) with every core filled.
How many courses of block is a 6 foot wall?
Nine. A standard block is 8 inches high including the mortar joint, so a 6 foot wall (72 inches) is 72 divided by 8, which is 9 courses. A height that is not a multiple of 8 inches rounds up to the next whole course, and the calculator shows the course count.
Can I use this for a retaining wall or a house foundation?
Use it for the block count and mortar only, and not as a design. The tool is meant for garden walls, planters and foundations of small structures. Retaining walls, load-bearing walls and anything that holds up a structure are engineered: reinforcement, grout spacing, footing size and height limits come from your local building code and the plans, and the core fill option here is a quantity, not a recommendation.
Sources & further reading
The 5 percent waste allowance, the 119 units per 100 square feet, the mortar bag yields for masonry cement and portland cement, the 240 blocks per ton of sand and the face shell bedding assumption are from the Concrete Masonry & Hardscapes Association’s (NCMA) TEK 04-02A, Estimating Concrete Masonry Materials. Blocks per square foot for the standard and half-high block, the mortar cross-check and the core fill volumes by thickness are from Titan America’s Block Estimating Guide, which describes its figures as rule-of-thumb. The pre-blended mortar yield of up to 13 standard 8 by 8 by 16 inch blocks per 80 lb bag is from the QUIKRETE data sheets for Mortar Mix (Type N) and Mason Mix (Type S). For how we source and check the numbers on every calculator, see our methodology page, and for the full topic see the complete guide to lawn and landscaping.
