How many concrete blocks do I need per square foot?

A standard 8 × 8 × 16 in block takes a 16 × 8 in module with its 3/8 in joints, so 1.125 blocks cover 1 sq ft of wall, or 113 per 100 sq ft. The 6 in and 12 in wide blocks have the same 8 × 16 in face and so the same count; a half-height 8 × 4 × 16 in block is 2.25 per sq ft. Multiply by the net wall area, add 5 to 10% for cuts and breakage, and round up.

How do I calculate blocks for a wall with doors and windows?

Multiply the wall length by its height, take off the area of each door and window (use the opening button), and count blocks for what is left. For example a 20 × 8 ft wall with a 3 × 7 ft door is 139 sq ft and 165 blocks with 5% extra. Blocks cut around openings and at the ends are what the extra is for. Lintel, jamb and corner units are not counted separately.

How much mortar do I need for concrete blocks?

Quikrete's data sheet for Mason Mix (No. 1136) says an 80 lb bag lays up to 13 standard 8 × 8 × 16 in blocks, so 100 blocks take at least 8 bags, and about 9 with the 10% the calculator adds because "up to" is a best case. The example 24 × 8 ft wall takes 20 bags. Check the rate on the bag you buy, since other brands and types lay a different number.

How much grout does it take to fill the cores?

For 8 in block, fully grouted, published yields are 1.12 cu yd per 100 sq ft of wall, about 0.27 cu ft per block (one cu yd per 100 blocks); grouting every 3rd core (24 in on center) takes 0.5 cu yd per 100 sq ft. The 24 × 8 ft example fully grouted takes 2.2 cu yd, or 97 bags of 80 lb concrete mix at 0.60 cu ft. Above about a cubic yard it is easier to order ready-mix or bulk grout. The yields come from a supplier's table; your supplier's figure may differ a little (estimate).

Which cores should be grouted, and do I need rebar?

That is a structural question and depends on the wall: its height, the soil or wind load behind it, and local code. A short freestanding garden wall, a retaining wall and a foundation wall are very different. The engineer or the building department specifies the rebar size and spacing, which cores are grouted and whether bond-beam courses are needed. This calculator only works out the material for the pattern you pick, and does not count the rebar or bond-beam units.

What is the difference between nominal and actual block size?

An 8 × 8 × 16 in block is its nominal size, which includes the 3/8 in mortar joint. The block itself is 7 5/8 × 7 5/8 × 15 5/8 in, so with a joint it fills 8 × 16 in of wall face. The same idea applies to the 6 in and 12 in wide blocks and the half-height 8 × 4 × 16 in unit, 3 5/8 in tall. Metric blocks are usually 440 × 215 mm with 10 mm joints on a 450 × 225 mm module.

How much extra should I order?

About 5% for a plain wall, 10% when there are many cuts, corners or openings. For example a 30 × 4 ft wall of 6 in blocks with 10% extra takes 149 blocks. Mortar bags are rounded up once for the whole job from the blocks you buy, and 113 blocks per 100 sq ft is the figure before any extra.

Does this calculator work for a retaining wall or foundation?

It counts blocks, mortar and grout for any block wall in running bond, but it is a material estimate and not a structural design. Dry-stack landscape blocks have their own calculator, and a poured concrete wall is a different one. A foundation or retaining wall of CMU needs a footing and reinforcement specified by an engineer or local code.

Concrete Block (CMU) Wall Calculator: Blocks, Mortar and Grout

A concrete block wall 24 ft long and 8 ft high (192 sq ft) in standard 8 × 8 × 16 in blocks with 3/8 in joints needs 227 blocks with 5% extra: 1.125 blocks per sq ft of wall, because each block takes a 16 × 8 in module. Mortar: 20 bags of 80 lb premixed Type N or S mortar, from Quikrete's published rate of up to 13 blocks per 80 lb bag with 10% added. If the cores are grouted, pick the pattern and the calculator adds the grout; fully grouted, this wall takes about 2.2 cu yd, or 97 bags of 80 lb concrete mix. This is a material estimate, not structural design.

Figures based on the sources listed belowUpdated 2026-10-04How we calculate

Wall length

Wall height

Extra blocks

Typical: cuts and breakage (5%)Many cuts or openings (10%)Exact (0%)Custom

Block sizeNominal size is width × height × length including the joint; the block itself is 3/8 in smaller. A 190 mm metric block is treated as 8 in wide for the grout. Check the block you are buying.

Mortar allowanceAdded on top of the manufacturer’s laying rate, which is a best case (“up to 13 blocks per 80 lb bag”). An estimate: droppings, furrowed beds and waste vary with the mason and the weather.

Grout the cores?Walls with rebar have the cores around each bar filled with grout. Whether and where is set by the engineer or local code; this only estimates the material. Bond-beam courses are not counted.

Price per block (optional)

Buy 227 blocks

192 sq ft + 5% waste = 201.60 sq ft

Blocks per 100 sq ft of wall (before extra): 113 blocks
Mortar mix (premixed Type N or S, 80 lb bags): 20 bags (joints ≈ 2.8 cu ft)

Low

$397.25

Expected

$567.50

High

$794.50

Includes 9.60 sq ft waste

How this number is calculated

192 sq ft + 5% waste = 201.60 sq ft ÷ 0.889 sq ft per block = 227 blocks

Shopping list

Brick and block trowel
Mason’s line and line blocks
Mortar mixing tub
Block chisel and brick hammer
4 ft level
Jointing tool (concave)

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Blocks and mortar per 100 sq ft of wall by block size

100 sq ft of wall, no extra blocks, worked by this calculator at build time: 14,400 ÷ ((length + joint) × (height + joint)) blocks. Bags are 80 lb premixed mortar from Quikrete's rate of up to 13 8 × 8 × 16 in blocks per bag, scaled for the block, with a 10% allowance (an estimate). The joint volume is geometric and shown for information.
Block	Blocks per sq ft	Blocks per 100 sq ft	Joint volume (cu ft)	Mortar bags (80 lb)
8 × 8 × 16 in	1.125	113	1.4	10
6 × 8 × 16 in	1.125	113	1.4	10
12 × 8 × 16 in	1.125	113	1.4	10
8 × 4 × 16 in half-height	2.25	225	2.4	16
440 × 215 × 190 mm	0.918	92	1.4	10

Core fill grout per 100 sq ft of wall by block width

Cu yd of grout per 100 sq ft of two-core block wall (Fairbanks Materials table), with the bags of 80 lb concrete mix at 0.60 cu ft each, worked by this calculator at build time. Every 2nd, 3rd or 4th core is 16, 24 or 32 in on center. Which cores are grouted comes from the engineer or the local code. Material estimate, not structural design.
Cores grouted	6 in wide	8 in wide	12 in wide
Fully grouted	0.93 cu yd, 42 bags	1.12 cu yd, 51 bags	1.73 cu yd, 78 bags
Every 2nd core, 16 in o.c.	0.55 cu yd, 25 bags	0.65 cu yd, 30 bags	1.01 cu yd, 46 bags
Every 3rd core, 24 in o.c.	0.42 cu yd, 19 bags	0.5 cu yd, 23 bags	0.76 cu yd, 35 bags
Every 4th core, 32 in o.c.	0.35 cu yd, 16 bags	0.43 cu yd, 20 bags	0.64 cu yd, 29 bags

Methodology & assumptions

Blocks per sq ft = 144 ÷ ((L + j) × (H + j)), with the block face length L, face height H and joint j in inches, the same formula the brick calculator uses. A US nominal 8 × 8 × 16 in block is 7 5/8 × 7 5/8 × 15 5/8 in as laid, so with a 3/8 in joint it sits on a 16 × 8 in module (128 sq in), and 144 ÷ 128 = 1.125 blocks per sq ft. Net wall area is the length × height less the doors and windows; blocks = net area × blocks per sq ft × (1 + extra), rounded up once. Running bond is assumed, with no corner or lintel units counted separately; bond-beam courses are out of scope. Mortar bags follow the manufacturer's laying rate. The Quikrete Mason Mix data sheet (No. 1136) says an 80 lb bag lays up to 13 standard 8 × 8 × 16 in blocks. For other blocks the rate is scaled with the brick calculator's method: the mortar in the joints around one block relative to an 8 × 8 × 16 block at 3/8 in, bags = blocks ÷ 13 × that factor × (1 + allowance), rounded up once. A hollow block is bedded on its two face shells, not across its whole width, so the bedded depth is taken as two face shells of 1.25 in (the ASTM C90 minimum), whatever the width: a 6 in, 8 in or 12 in wide block takes about the same mortar, and a half-height block takes less per block (but there are twice as many). That is an estimate; mortar on webs, wider joints or full bedding take more. Because "up to" is a best case, an allowance is added on top: 10% by default, or none, or 25% (estimates; droppings, furrowed beds and mortar left in the tub vary with the mason and the weather). The joint volume shown beside the bag count is geometric and for information only. Core fill: grout volume comes from published yields per 100 sq ft of wall for two-core block, by nominal width and by how often cores are grouted: 1.12 cu yd per 100 sq ft fully grouted for an 8 in wall, which is 0.27 cu ft per block, about the volume of the two cores plus a little for spillage. The yields are per sq ft of wall, so half-height blocks use the same figure, and a 190 mm metric block is read as 8 in. The grout is shown in cu yd and in bags of concrete mix (0.60, 0.45 or 0.30 cu ft for 80, 60 and 40 lb); bagged core-fill grout yields can differ, so check yours, and for a tall wall ready-mix grout by the truck is the usual choice. Which cores are grouted, the rebar and the bond beams come from the engineer's drawings or the local code, so this is an estimate of material only, not a design. The metric toggle shows lengths in m.

Quikrete, DATA SHEET Mason Mix 1136: an 80 lb bag lays up to 37 standard bricks or 13 standard 8 × 8 × 16 in blocks
Fairbanks Materials, "Grout Calculations for Concrete Blocks": cubic yards of grout per 100 sq ft of wall for 6, 8, 10 and 12 in two-core block, all cells filled and at 16, 24 and 32 in on center
Westbrook Concrete Block Co., "Fine Core Fill Grout Yields": 1 cu yd of grout fills 100 8 in blocks, fully grouted (agrees with the 1.12 cu yd per 100 sq ft above)
NCMA TEK 2-1B (CMHA), Typical Sizes and Shapes of Concrete Masonry Units, and ASTM C90, Loadbearing Concrete Masonry Units: nominal and actual sizes (7 5/8 × 7 5/8 × 15 5/8 in for an 8 × 8 × 16) and the 1 1/4 in minimum face shell thickness
ASTM C270, Standard Specification for Mortar for Unit Masonry (Types N, S, M and O)
Concrete block price: product listings for 8 × 8 × 16 in concrete block at The Home Depot (about $1.78 to $2.78 each when checked); the price range and the 10% mortar allowance are estimates, not from a single document
Metric block, 440 × 215 mm face with 10 mm joints on a 450 × 225 mm module and a 190 mm width: a common size, assumed (check the block you buy); the 190 mm width is read as 8 in for the grout (an assumption)

How to calculate concrete blocks, mortar and grout for a wall

Measure the wall. Measure the length and height of each wall in feet (decimals), and the doors and windows to take off.
Pick the block. Use the nominal size on the block: 8 × 8 × 16 in is the standard. Check the width for the 6 in and 12 in units, or the half-height block.
Count the blocks. A 8 × 8 × 16 in block covers 8 × 16 in of wall with its joints, so 1.125 blocks per sq ft. Multiply by the net wall area and add 5 to 10% for cuts and breakage.
Work out the mortar. An 80 lb bag of premixed mortar lays up to 13 standard blocks (Quikrete Mason Mix data sheet). Divide the blocks by 13 and add about 10% because 13 is a best case.
Add the grout if the cores are filled. Take the grout from the published yield for your block width and core pattern, per 100 sq ft of wall, and divide by the yield of a bag of concrete mix or order it by the cubic yard. The pattern comes from the engineer or the local code.
Round up. Round the bags up once for the whole job, and check the rate printed on the bag you buy.

Worked examples

Project	Result
24 ft long, 8 ft high wall, 8 × 8 × 16 in blocks, 3/8 in joints, cores not filled	192 sq ft + 5% extra → 227 blocks, 20 bags of mortar
24 ft long, 8 ft high wall, 8 × 8 × 16 in blocks, every core grouted	192 sq ft + 5% extra → 227 blocks, 20 bags of mortar, 2.2 cu yd of grout (97 bags)
20 ft long, 8 ft high wall with a 3 × 7 ft door, 8 × 8 × 16 in blocks, every 3rd core grouted	139 sq ft + 5% extra → 165 blocks, 14 bags of mortar, 0.7 cu yd of grout (32 bags)
30 ft long, 4 ft high garden wall, 6 × 8 × 16 in blocks	120 sq ft + 10% extra → 149 blocks, 13 bags of mortar
12 ft long, 3 ft high wall, 8 × 4 × 16 in half-height blocks	36 sq ft + 5% extra → 86 blocks, 7 bags of mortar
18 ft long, 8 ft high wall, metric 440 × 215 mm blocks, 10 mm joints	144 sq ft + 5% extra → 139 blocks, 14 bags of mortar

Frequently asked questions

How many concrete blocks do I need per square foot?: A standard 8 × 8 × 16 in block takes a 16 × 8 in module with its 3/8 in joints, so 1.125 blocks cover 1 sq ft of wall, or 113 per 100 sq ft. The 6 in and 12 in wide blocks have the same 8 × 16 in face and so the same count; a half-height 8 × 4 × 16 in block is 2.25 per sq ft. Multiply by the net wall area, add 5 to 10% for cuts and breakage, and round up.
How do I calculate blocks for a wall with doors and windows?: Multiply the wall length by its height, take off the area of each door and window (use the opening button), and count blocks for what is left. For example a 20 × 8 ft wall with a 3 × 7 ft door is 139 sq ft and 165 blocks with 5% extra. Blocks cut around openings and at the ends are what the extra is for. Lintel, jamb and corner units are not counted separately.
How much mortar do I need for concrete blocks?: Quikrete's data sheet for Mason Mix (No. 1136) says an 80 lb bag lays up to 13 standard 8 × 8 × 16 in blocks, so 100 blocks take at least 8 bags, and about 9 with the 10% the calculator adds because "up to" is a best case. The example 24 × 8 ft wall takes 20 bags. Check the rate on the bag you buy, since other brands and types lay a different number.
How much grout does it take to fill the cores?: For 8 in block, fully grouted, published yields are 1.12 cu yd per 100 sq ft of wall, about 0.27 cu ft per block (one cu yd per 100 blocks); grouting every 3rd core (24 in on center) takes 0.5 cu yd per 100 sq ft. The 24 × 8 ft example fully grouted takes 2.2 cu yd, or 97 bags of 80 lb concrete mix at 0.60 cu ft. Above about a cubic yard it is easier to order ready-mix or bulk grout. The yields come from a supplier's table; your supplier's figure may differ a little (estimate).
Which cores should be grouted, and do I need rebar?: That is a structural question and depends on the wall: its height, the soil or wind load behind it, and local code. A short freestanding garden wall, a retaining wall and a foundation wall are very different. The engineer or the building department specifies the rebar size and spacing, which cores are grouted and whether bond-beam courses are needed. This calculator only works out the material for the pattern you pick, and does not count the rebar or bond-beam units.
What is the difference between nominal and actual block size?: An 8 × 8 × 16 in block is its nominal size, which includes the 3/8 in mortar joint. The block itself is 7 5/8 × 7 5/8 × 15 5/8 in, so with a joint it fills 8 × 16 in of wall face. The same idea applies to the 6 in and 12 in wide blocks and the half-height 8 × 4 × 16 in unit, 3 5/8 in tall. Metric blocks are usually 440 × 215 mm with 10 mm joints on a 450 × 225 mm module.
How much extra should I order?: About 5% for a plain wall, 10% when there are many cuts, corners or openings. For example a 30 × 4 ft wall of 6 in blocks with 10% extra takes 149 blocks. Mortar bags are rounded up once for the whole job from the blocks you buy, and 113 blocks per 100 sq ft is the figure before any extra.
Does this calculator work for a retaining wall or foundation?: It counts blocks, mortar and grout for any block wall in running bond, but it is a material estimate and not a structural design. Dry-stack landscape blocks have their own calculator, and a poured concrete wall is a different one. A foundation or retaining wall of CMU needs a footing and reinforcement specified by an engineer or local code.

Handy tools

Feet and Inches Calculator: Turn a tape reading in feet, inches and fractions into the decimal feet the wall length and height fields take.