Concrete Block Calculator
Blocks for a wall from its size and the block face, with doors and windows taken out, and mortar or grout bags from a maker’s stated yield or your own figure.
The working
Gross area = Wall length × Wall height
= 20 ft × 8 ft
= 160 sq ft
Blocks = Net area × 144 ÷ Face area in sq in
Blocks laid
blocks
Waiting on you
Choose a block face, or enter your own block’s face length and height from your supplier.
- Net wall area
- 160ft²
Enter the wall’s length and height, or its area, and any doors and windows. Choose the nominal 8 × 16 in face, the half-high 4 × 16 in face, or enter your own block. The calculator counts blocks by area, rounds up once to whole blocks, checks the count course by course, and adds only the allowance you enter. Mortar and grout bags come from the figure on your bag, or from a manufacturer’s published yield for a standard 8 in block.
How this calculator works
Only your inputs and exact unit conversions. Where a figure comes from anywhere else, it is recorded below with its source.
- Formula version
- 1.0.0
- Last reviewed
- 2026-09-29
- External data
- 14 sources
- Category
- Materials
What this calculates
The number of concrete blocks in a single-wythe wall, one block thick. The count comes from the wall’s area and the area of one block face with its joint. Doors and windows come out first, and the answer is rounded up once to whole blocks. Mortar bags, grout volume and grout bags follow from the block count when there is a yield per bag or a volume per block to divide by.
“Cinder block” is one of the everyday names for a concrete masonry unit. CMHA’s answer to the question (CMU-FAQ-014-14, revised 2014) says concrete masonry units are known as “concrete block”, “cinder block”, “CMU” or simply “block”, calls the two essentially the same product, and says a block’s density does not show whether it was made with cinders. The count here depends on the face size only.
Why 1.125 blocks per square foot
A standard concrete block has a nominal face 8 in high by 16 in long (CMHA CMU-TEC-001-23 §3.1.1). Nominal means the block plus one mortar joint: CMHA says specified dimensions are typically 3/8 in less than nominal, so that an 8 in module is kept with 3/8 in joints. One nominal face covers 16 × 8 = 128 sq in.
A square foot is 12 × 12 = 144 sq in, so a square foot of wall takes 144 ÷ 128 = 1.125 blocks, and one block covers 128 ÷ 144 = 8/9 = 0.888889 sq ft. That is all the 1.125 is. In metric the same face is 0.4064 m × 0.2032 m, and 1 ÷ (0.4064 × 0.2032) = 12.1094 blocks per m².
Blocks = Net area × 144 ÷ Face area in sq in. The count is printed exactly, then rounded up once, at the end. A half-high 4 × 16 in face covers 64 sq in: 144 ÷ 64 = 2.25 blocks per square foot, 24.2188 per m².
Nominal and actual sizes: the joint is counted once
A block sold as 8 × 8 × 16 is typically 7 5/8 × 7 5/8 × 15 5/8 in (CMHA; Angelus Block’s precision units are drawn at those sizes). Laid with a 3/8 in joint it takes up 8 × 16 in of wall face. The joint belongs with a measured, actual size, never with a nominal one.
Adding a 3/8 in joint to the nominal 16 × 8 in counts it twice: 16.375 × 8.375 = 137.140625 sq in, which gives 105.0017 blocks per 100 sq ft instead of 112.5, 6.67% short.
Not every unit follows the rule: CMHA says “typically”, and Angelus lists an 8 × 2 × 16 unit whose actual height is 2 in. For any other block, a metric block or a joint other than 3/8 in, choose your own block face and say whether your sizes are nominal, with one joint in them, or actual, in which case the joint you enter is added once to the length and once to the height.
CMHA summarises ASTM C90 as allowing overall dimensions to vary by no more than ±1/8 in from the specified size. ASTM C90 itself is sold and was not read for this page.
Doors, windows and the course check
Each size of opening is count × width × height, and all of them come off the gross wall area before blocks are counted, as CMHA TEK 04-02A does. The TEK also says pilaster, corner and bond-beam units are to be calculated separately and subtracted from the total; this count treats every unit as a plain block.
With length and height, the calculator also counts course by course: courses = wall height ÷ face height and blocks per course = wall length ÷ face length, each rounded up, because a part course or a part block still uses a unit cut on site. On a wall that fits the module the two methods agree: 8 ft is 96 ÷ 8 = 12 courses, 20 ft is 240 ÷ 16 = 15 blocks, and 12 × 15 = 180, the same as 160 sq ft × 144 ÷ 128. On a 25 × 7 ft wall they do not: 300 ÷ 16 = 18.75, so 19 per course, and 84 ÷ 8 = 10.5, so 11 courses, 209 blocks, against 175 × 144 ÷ 128 = 196.875, or 197, by area. Both numbers are shown.
The course check is on the gross wall, with no openings taken out, and it does not model running-bond half units or cut ends.
- Courses of an 8 in face, by wall height: 2 ft, 24 ÷ 8 = 3; 3 ft, 36 ÷ 8 = 4.5; 4 ft, 48 ÷ 8 = 6; 6 ft, 72 ÷ 8 = 9; 8 ft, 96 ÷ 8 = 12; 10 ft, 120 ÷ 8 = 15; 12 ft, 144 ÷ 8 = 18. A 4 in face doubles each.
Waste allowance and price
Both are yours, optional and blank. No allowance is assumed: breakage and cuts depend on the block, the layout and the crew. With an allowance, blocks to order = exact blocks × (1 + allowance ÷ 100), rounded up once. The allowance is never added to mortar or grout. With a price per block, the cost is the blocks to order, or the whole blocks laid if there is no allowance, times your price.
CMHA TEK 04-02A prints 119 units per 100 ft² for the 8 × 16 in face, including a 5 percent allowance for waste and breakage. It is quoted, not applied: the count here is 112.5 per 100 sq ft before any allowance.
Mortar
Mortar bags = whole blocks ÷ blocks per bag, rounded up. The yield per bag is printed on the bag or in its data sheet. It changes with the product, the bag, the block and how the mortar is laid, so the calculator uses your figure, or a manufacturer’s stated one that you choose.
QUIKRETE’s yields are stated for a standard 8 × 8 × 16 in block. Sakrete’s are stated for an “8" (200 mm) concrete block”, with no face size. Both are offered only with the 8 × 16 in face and the 8 in width. QUIKRETE Mortar Mix No. 1102 (Type N) and Mason Mix No. 1136 (Type S): an 80 lb bag lays “up to” 13 standard 8 × 8 × 16 in blocks (data sheets revised November 2020). “Up to” is a maximum, so the result is the fewest bags, and the sheets do not say whether they allow for waste. Sakrete Mortar Mix Type S (Rev. 05/18): 6, 9 or 12 “8" (200 mm) concrete block” per 40, 60 or 80 lb bag, approximate, and “the yield above does not allow for waste and spillage”.
A QUIKRETE mortar yield for its 10, 40, 60 or 94 lb or its 25 or 30 kg bags was not found in the sources reviewed, and the 80 lb figure is not prorated to them. A QUIKRETE or Sakrete mortar or grout yield for any block other than the 8 in blocks named above was not found in the sources reviewed. An older QUIKRETE Mortar Mix sheet (2007, still hosted) printed 6, 9 and 12 standard blocks per 40, 60 and 80 lb bag; the current sheet states up to 13 for the 80 lb bag and nothing for the others.
QUIKRETE’s Concrete Block Construction sheet (2006) describes joints “about 3/8" thick”, a full bed of mortar under the first course and mortar on the horizontal face shells of each block above it. Neither QUIKRETE yield sentence says which bedding it assumes.
No mortar type is recommended here. The QUIKRETE sheets refer to “Appendix XI of ASTM C270” for choosing one; that standard is sold and was not read.
Core fill
Grout volume = blocks filled × the grout one block takes, and grout bags = blocks filled ÷ blocks per bag, rounded up. Which cells to fill is set by your plans or your engineer; nothing is suggested here. A manufacturer’s core volume per block was not found in the sources reviewed, so the volume per block is yours, from your block maker or measured. The volume is printed in cubic feet, in cubic yards (÷ 27) and in cubic metres (× 0.028316846592, because 1 ft = 0.3048 m exactly).
QUIKRETE Core-Fill Grout, Coarse No. 1585-07 and Fine No. 1585-08 (data sheets revised November 2024): an 80 lb bag yields approximately 0.65 or 0.68 ft³ and fills the cores of approximately 3 standard 8 × 8 × 16 in blocks. These can be chosen with the 8 × 16 in face and the 8 in width, and should be read beside the sources: 0.65 ÷ 3 = 0.216667 cu ft (374.4 cu in) per block, while CMHA’s worked example for an 8 in unit at the ASTM C90 minimum shells and webs takes 548.4 cu in, so 0.65 cu ft would fill 0.65 × 1,728 ÷ 548.4 = 2.0481 of those units. CMHA TEK 04-02A Table 3 gives 36.1 ft³ per 100 ft² of fully grouted 8 in wall: 36.1 ÷ 112.5 = 0.320889 cu ft per block with 3% waste, or 2.0256 blocks per 0.65 cu ft.
What the sources say about mortar and grout (quoted, not applied)
Each has a record below. Ranges are never averaged, and none of these figures enters a result.
- SPEC MIX Mortar Cement & Sand, blocks per 80 lb bag, “Yields include typical waste”: 4 in 15–17; 6 in 12–14; 8 in 11–13; 10 in 11–13; 12 in 10–12. SPEC MIX says FL, CA, OR and WA “experience higher yields”.
- CMHA TEK 04-02A: about 30 hollow units per 70 lb bag of masonry cement with face-shell bedding, and 1 ton of sand per 8 bags, 240 units; preblended mortar, 16 units per 80 lb bag and 420 per 3,000 lb bag; about 62 hollow units per 94 lb bag of portland cement mixed with lime and sand. Table 2 says its values include nominal amounts for waste and assume face-shell bedding.
- Sakrete Masonry Cement Type S (Rev. 04/20), mixed 1 part to 3 parts sand: 38 blocks per 75 lb bag and 40 per 78 lb bag, in a column headed “8" (416 mm) Blocks”. The header’s units conflict (8 in is about 203 mm, and 416 mm is about 16.4 in), and no bedding or waste basis is given.
- QUIKRETE bulk (©2018): a 3,000 lb mortar bag lays “up to 530 standard blocks”; a 3,000 lb grout bag fills approximately 110 (fine) or 105 (coarse) standard 8 × 8 × 16 in blocks.
- CMHA TEK 04-02A Table 3, grout per 100 ft² of wall with every cell grouted, two-core units, 3% waste: 6 in 25.6 ft³; 8 in 36.1; 10 in 47.0; 12 in 58.9; 14 in 74.5. Table 4, preblended grout, 80 lb bag of approximately 0.66 ft³, headed “number of cores”: 6 in 3.6; 8 in 2.7; 10 in 2.2; 12 in 1.8. Its 3,000 lb figure for 8 in, 110, equals QUIKRETE’s 110 blocks, so whether it counts cores or blocks is unclear. The TEK does not recommend grouting conventional 4 in units.
- SPEC MIX Core Fill Grout, blocks filled per 80 lb bag, including typical waste: 6 in 3.4–3.8; 8 in 2.5–2.9; 10 in 2.1–2.3; 12 in 1.7–1.9. SPEC MIX’s submittal is certified by QUIKRETE’s Technical and Engineering Center, so it is not independent of the QUIKRETE figures.
- CMHA CMU-TEC-002-23 worked example, grout per 8 in unit at ASTM C90 minimum dimensions: 2 × (7.625 − 1.25 − 1.25) × ((15.625 − 3 × 0.75) ÷ 2) × (7.625 + 0.375) = 548.4 cu in, over a course height that includes the 3/8 in bed joint.
What it does not decide
No bond layout or cut list, no reinforcement, no footing, no mortar type, no grout spacing and no structural check. Those come from your plans, your building department and your engineer. Retaining wall units and brick are not counted here.
A 30 × 6 ft wall with two 4 × 3 ft windows
The wall, the windows, the 5% allowance, the block face and the mortar product are example inputs, not recommendations. The face is CMHA’s nominal 8 × 16 in, with the 8 in width chosen under Makers’ yields. The mortar is the Sakrete Mortar Mix Type S 80 lb option: approx. 12 “8" (200 mm) concrete block” per bag.
- Wall
- 30 ft × 6 ft
- Windows
- 2 × 4 ft × 3 ft
- Block face
- 8 × 16 in nominal (128 sq in)
- Block width
- 8 in nominal
- Your allowance
- 5%
- Mortar
- Sakrete Mortar Mix Type S, 80 lb: approx. 12 “8" (200 mm) concrete block” per bag
- 01Gross area= 30 × 6= 180 sq ft
- 02Windows= 2 × 4 × 3= 24 sq ft
- 03Net area= 180 − 24= 156 sq ft
- 04Blocks= 156 × 144 ÷ 128= 175.5
- 05Whole blocks= 175.5, rounded up= 176 blocks
- 06Course check, gross wall= 72 ÷ 8 = 9 courses; 360 ÷ 16 = 22.5, rounded up to 23; 9 × 23= 207 blocks, windows not taken out
- 07To order with your 5%= 175.5 × 1.05 = 184.275, rounded up= 185 blocks
- 08Mortar bags= 176 ÷ 12 = 14.666667, rounded up= 15 bags
176 laid, 185 to order with your 5%; 15 bags of mortar
Blocks per area, by nominal face
Before any allowance and before doors and windows. Each cell is 144 ÷ the face area in sq in, times the area; per m², 1 ÷ (face length in m × face height in m). The two faces are CMHA’s nominal faces (CMU-TEC-001-23 §3.1.1, recorded below).
| Nominal face | Face area | Blocks per sq ft | Per 100 sq ft | Per 1,000 sq ft | Per m² |
|---|---|---|---|---|---|
| 8 × 16 in | 128 sq in (0.888889 sq ft) | 1.125 | 112.5 | 1,125 | 12.1094 |
| 4 × 16 in (half-high) | 64 sq in (0.444444 sq ft) | 2.25 | 225 | 2,250 | 24.2188 |
CMHA TEK 04-02A prints 119 units per 100 ft² for the 8 × 16 in face, which includes a 5 percent allowance for waste and breakage; it is quoted, not applied. Adding a 3/8 in joint to the nominal 16 × 8 in counts it twice: 16.375 × 8.375 = 137.140625 sq in, 105.0017 per 100 sq ft, 6.67% short.
What it assumes
- 01A single-wythe wall: one block thick.
- 02Every block has the same face, laid in courses of that face’s height.
- 03Doors and windows are rectangles, taken out of the gross area.
- 04The count is by area and rounded up once; the course check uses the gross wall.
- 05Waste, prices, blocks per bag and grout per block apply only when you enter or choose them.
- 06Mortar and grout use the whole blocks laid, never your allowance.
What it does not do
- No bond layout or cut list: running-bond half units, cut ends and closures are not modelled.
- Where two walls meet, measuring both to the outside corner counts the corner twice: wall thickness × height.
- Pilaster, corner and bond-beam units are to be calculated separately and subtracted from the total (CMHA TEK 04-02A); this count treats every unit as a plain block.
- No reinforcement, footing, mortar type, grout spacing or structural advice.
- Retaining wall units and brick are not counted.
- The makers’ mortar and grout yields are offered only with the 8 × 16 in face and the 8 in width. QUIKRETE’s are stated for a standard 8 × 8 × 16 in block. Sakrete’s are stated for an “8" (200 mm) concrete block”. For any other block, use the figure on your bag.
Common questions.
- How do I calculate how many concrete blocks I need?
- Work out the wall’s area in square feet and take out the doors and windows. Multiply by 144 and divide by the area of one block face in square inches, joint included. For the nominal 8 × 16 in face that is 144 ÷ 128 = 1.125 blocks per square foot. Round up once, at the end, and add any allowance you choose on top.
- How many blocks do I need for a 20 × 8 ft wall?
- 160 sq ft × 144 ÷ 128 = 180 blocks with the 8 × 16 in face, before any allowance. Course by course it is the same: 8 ft is 96 ÷ 8 = 12 courses, 20 ft is 240 ÷ 16 = 15 blocks, and 12 × 15 = 180. Take out a 3 × 7 ft door and the wall is 160 − 21 = 139 sq ft: 139 × 144 ÷ 128 = 156.375, so 157 whole blocks.
- How many square feet does a cinder block cover?
- A block with the nominal 8 × 16 in face covers 16 × 8 = 128 sq in with its joint, which is 128 ÷ 144 = 8/9 = 0.888889 sq ft. The other way round, a square foot takes 144 ÷ 128 = 1.125 blocks. A half-high 4 × 16 in face covers 64 sq in, 0.444444 sq ft.
- How many blocks are needed for 1,000 square feet of wall?
- 1,000 × 144 ÷ 128 = 1,125 blocks with the 8 × 16 in face, before any allowance and before doors and windows come out. With the half-high 4 × 16 in face it is 1,000 × 144 ÷ 64 = 2,250. CMHA TEK 04-02A prints 119 units per 100 ft² for the 8 × 16 face, including a 5 percent allowance for waste and breakage; that figure is quoted, not applied.
- How many bags of mortar (or cement) do I need for 100 or 1,000 blocks?
- It depends on the mortar, the bag and the block, so the answer is the bag’s own figure. QUIKRETE Mortar Mix No. 1102 and Mason Mix No. 1136 lay up to 13 standard 8 × 8 × 16 in blocks per 80 lb bag, so 100 ÷ 13 = 7.69, at least 8 bags, and 1,000 ÷ 13 = 76.92, at least 77. Sakrete Mortar Mix Type S lays approximately 12 “8" (200 mm) concrete block” per 80 lb bag, with nothing allowed for waste: 100 ÷ 12 = 8.33, so 9 bags, and 1,000 ÷ 12 = 83.33, so 84. For mortar mixed on site from masonry cement and sand, two figures were read and are quoted, not applied: Sakrete Masonry Cement Type S prints 38 blocks per 75 lb bag and 40 per 78 lb bag, mixed 1 to 3 with sand, in a column whose header mixes 8 in with 416 mm; CMHA TEK 04-02A says one 70 lb bag of masonry cement lays approximately 30 hollow units with face-shell bedding, waste included.
- Why is an 8x8x16 block not 8 × 8 × 16 inches?
- Because 8 × 8 × 16 is its nominal size: the block plus one mortar joint. CMHA says specified dimensions are typically 3/8 in less than nominal, so blocks laid with 3/8 in joints keep an 8 in module, and Angelus Block’s precision 8 × 8 × 16 unit is drawn at 7 5/8 × 7 5/8 × 15 5/8 in. Not every unit follows it: Angelus lists an 8 × 2 × 16 whose actual height is 2 in. CMHA summarises ASTM C90 as allowing ±1/8 in on the specified dimensions; the standard itself is sold and was not read.
- Do I add the mortar joint to the block size?
- Only to an actual, measured size. A nominal size already includes one joint, and adding it again counts it twice: 16.375 × 8.375 = 137.140625 sq in instead of 128, which gives 105.0017 blocks per 100 sq ft instead of 112.5, 6.67% short. Choose your own block face and say which kind of size you have; the calculator adds your joint once to the length and once to the height of an actual size.
- What is the difference between a cinder block and a concrete block?
- For counting, none. CMHA (CMU-FAQ-014-14, revised 2014) says concrete masonry units are known as “concrete block”, “cinder block”, “CMU” or simply “block”, that the two are essentially the same product, made of water, cement and aggregate, and that a block’s density does not show whether it was made with cinders. The count here depends on the face size only.
- Does the width of the block change the count?
- No. CMHA TEK 04-02A says its method for counting units is independent of the unit width, and so is this one: it uses the face only. The makers’ mortar and grout yields offered here are stated for 8 in blocks only, so they appear only with the 8 in width. Grout volume changes with width (CMHA TEK 04-02A Table 3; SPEC MIX’s core-fill table, both quoted in the method section).
- How many courses of block make an 8 ft wall?
- 96 in ÷ 8 in = 12 courses of 8 × 16 in block. A 4 ft wall is 48 ÷ 8 = 6 courses and a 10 ft wall 120 ÷ 8 = 15. A height that is not a multiple of 8 in leaves a part course: 3 ft is 36 ÷ 8 = 4.5 courses, and the half course still takes a row of units. With the half-high 4 in face, each count doubles.
- Is it cheaper to build with blocks or to pour a concrete wall?
- No prices are assumed here, so this page cannot say. Price the blocks with your supplier’s price per block, plus mortar and grout if you use them, and price a poured wall’s volume in the concrete calculator’s wall mode with your own ready-mix quote. Labour, forms and reinforcement are in neither.
- How much grout fills the cores of a block?
- It depends on the block’s cores, and a maker’s core volume per block was not found in the sources reviewed, so enter your own figure. The sources disagree. QUIKRETE Core-Fill Grout says approximately 3 standard 8 × 8 × 16 in blocks per 80 lb bag of approximately 0.65 ft³, which is 0.216667 cu ft per block. CMHA’s worked example at ASTM C90 minimum shells and webs gives 548.4 cu in per 8 in unit, so 0.65 ft³ fills 2.0481 units. CMHA TEK 04-02A Table 3 works out to 2.0256 blocks per 0.65 ft³ with 3% waste, and SPEC MIX gives 2.5 to 2.9 blocks per 80 lb bag including waste. All are listed in the method section.
- What about retaining wall blocks?
- They are a different product. CMHA names segmental retaining wall units as a related concrete product used in a different application, and this calculator does not count them.
- How much do 1,000 blocks cost?
- Enter your supplier’s price per block under Waste and price and the calculator multiplies it out; no price is assumed. 1,000 blocks at your price is 1,000 × that price, plus mortar and grout at your prices per bag.
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