At a glance
- Blocks per square foot
- 1.125
- Mortar
- 1 × 80 lb bag per 12 blocks
- Block price
- $1.25 – $5 each
- Installed wall
- $12 – $25 per sq ft
A 20 × 4 ft garden wall takes about 95 standard blocks and 8 bags of mortar: about $335 in materials or $1,500 installed.
How to calculate how many blocks you need
A standard concrete block is 8 in. high and 16 in. long on the wall, counting the mortar joint. That makes the math simple:
- Count the courses. Convert the wall height to inches and divide by 8. Round up, since you can't lay part of a course.
- Find the blocks per course. Convert the wall length to inches and divide by 16.
- Multiply courses × blocks per course.
- Subtract openings. Multiply the area of each door or window in sq ft by 1.125.
- Add 5% to 10% extra for broken blocks and cuts, and round up.
A quick shortcut: multiply the wall area in square feet by 1.125. A 100 sq ft wall needs about 113 blocks before extras.
Blocks for common wall sizes
| Wall (length × height) | Blocks* | 80 lb mortar bags | DIY materials | Installed |
|---|---|---|---|---|
| 10 × 4 ft (40 sq ft) | 48 | 4 | $170 | $740 |
| 20 × 4 ft (80 sq ft) | 95 | 8 | $335 | $1,500 |
| 20 × 6 ft (120 sq ft) | 142 | 12 | $500 | $2,200 |
| 30 × 4 ft (120 sq ft) | 142 | 12 | $500 | $2,200 |
| 50 × 6 ft (300 sq ft) | 355 | 29 | $1,250 | $5,550 |
| 100 × 4 ft (400 sq ft) | 473 | 38 | $1,650 | $7,400 |
| 40 × 8 ft (320 sq ft) | 378 | 30 | $1,300 | $5,900 |
*Standard 8 × 8 × 16 blocks, including 5% extra, with no openings or core fill. Costs are typical midpoints at average US prices.
Concrete block sizes
Blocks are named by their nominal size: width × height × length. The actual block is ⅜ in. smaller in each direction to leave room for the mortar joint.
| Nominal size | Actual size | Typical use | Price each |
|---|---|---|---|
| 4 × 8 × 16 | 3⅝ × 7⅝ × 15⅝ in. | Veneer, partitions, low garden walls | $1.25 – $3 |
| 6 × 8 × 16 | 5⅝ × 7⅝ × 15⅝ in. | Garden and screen walls | $1.50 – $3.50 |
| 8 × 8 × 16 | 7⅝ × 7⅝ × 15⅝ in. | Most walls, foundations, retaining walls | $1.50 – $4 |
| 10 × 8 × 16 | 9⅝ × 7⅝ × 15⅝ in. | Taller retaining and basement walls | $2 – $4.50 |
| 12 × 8 × 16 | 11⅝ × 7⅝ × 15⅝ in. | Heavy foundations and tall walls | $2.50 – $5 |
Split-face and other decorative blocks cost more, about $2.50 to $3.50 each, and segmental retaining wall blocks run $6 to $11 each.
How much mortar do you need?
Pre-mixed mortar has the sand already in the bag, so you only add water. According to Quikrete's data sheet:
- One 80 lb bag lays about 12 standard blocks.
- One 60 lb bag lays about 9 standard blocks.
So divide your block count by 12 for 80 lb bags. For large jobs, masons often mix their own mortar from bags of masonry cement and bulk sand, which costs less per block.
Filling the cores
Concrete blocks have two hollow cores. In walls that must resist soil pressure, wind or heavy loads, steel rebar is set in some cores, which are then filled with grout or concrete. The calculator uses these fill volumes:
| Block width | Fill per block | Fill per 100 blocks |
|---|---|---|
| 6 in. | 0.22 cu ft | 0.83 cu yd |
| 8 in. | 0.27 cu ft | 1.0 cu yd |
| 10 in. | 0.33 cu ft | 1.23 cu yd |
| 12 in. | 0.42 cu ft | 1.54 cu yd |
For the 20 × 4 ft example wall, rebar cores every 48 in. take about 7 bags of 80 lb concrete, every 32 in. about 11 bags, and filling every core about 41 bags (0.9 cu yd). Above about one cubic yard, ready-mix grout is usually easier; see our concrete cost calculator.
Don't forget the footing
Most block walls sit on a poured concrete footing, typically twice as wide as the block and at least 8 in. deep, set below the frost line in cold climates. For an 8 in. block wall that's a 16 × 8 in. footing, which takes about 0.9 cubic feet of concrete per foot of wall. The calculator shows this volume in the "What to buy" list but doesn't add it to the cost.
How much does a concrete block wall cost?
Most block walls cost $12 to $25 per square foot professionally installed, including blocks, mortar and labor. Sources range from $10 to $40 per sq ft, depending on the block, the height, the site and local wages. Labor is usually about half of the total.
- Blocks: $1.25 to $5 each for standard sizes.
- Labor: about $10 to $17 per sq ft, or $35 to $100 per hour.
- Rebar and core fill: adds about $2 to $8 per sq ft when every core is filled.
- Finishes: stucco or plaster adds about $3 to $9 per sq ft, paint about $0.65 to $3, and waterproofing sealant about $2 to $10.
- Permits: $200 to $2,000 for walls that need one, such as retaining walls over 3 to 4 ft.
DIY or hire a mason?
Building a block wall yourself can cut the cost by 70% or more, since you only pay for materials. But each 8 in. block weighs about 35 lb, the first course must be perfectly level, and walls that hold back soil or carry a load need proper footings and reinforcement. A short garden wall is a reasonable DIY project; retaining walls and foundations are best left to a pro.
Frequently asked questions
How many concrete blocks are in a square foot?
A standard block has an 8 × 16 in. face, including the mortar joint, so it takes 1.125 blocks to cover one square foot of wall. A 100 sq ft wall needs about 113 blocks, or about 119 with 5% extra for breakage and cuts.
How many blocks do I need for a 10 × 10 ft wall?
A 10 ft long, 10 ft high wall is 15 courses of 7.5 blocks, which is about 113 standard 8 × 16 blocks. With 5% extra, buy about 119 blocks.
How many bags of mortar do I need per block?
One 80 lb bag of pre-mixed mortar lays about 12 standard 8 × 8 × 16 blocks, and a 60 lb bag lays about 9, according to Quikrete. For 100 blocks, plan on about 9 bags of 80 lb mortar mix.
How much does a concrete block wall cost?
Most block walls cost about $12 to $25 per square foot professionally installed. A 20 ft long, 4 ft high wall costs about $1,500 installed ($960 to $2,000), or about $335 in blocks and mortar if you build it yourself.
What are the actual dimensions of an 8 × 8 × 16 block?
A standard 8 × 8 × 16 block actually measures 7⅝ × 7⅝ × 15⅝ in. The ⅜ in. mortar joint brings each block up to the nominal 8 × 16 in. on the wall.
Is a cinder block the same as a concrete block?
Today, almost all "cinder blocks" sold are concrete blocks, also called concrete masonry units or CMUs. True cinder blocks made with coal ash are rarely produced. The sizes and math are the same.
Do I need to fill the cores of a block wall?
Load-bearing walls, retaining walls and tall walls usually need rebar and grout in some or all cores, at a spacing set by your local code or an engineer. Short garden walls are often built with rebar cores every 32 to 48 in. Check with your building department before you build.
How we calculate
Block counts use the standard 8 × 16 in. block face (1.125 blocks per sq ft), with courses rounded up to whole rows. Openings are subtracted at 21 sq ft per door and 12 sq ft per window. Mortar uses Quikrete's coverage of 12 standard blocks per 80 lb bag and 9 per 60 lb bag; thinner blocks use a little less and wider blocks a little more. Core fill volumes come from Inch Calculator's grout fill table, and fill is converted to 80 lb concrete bags at 0.60 cu ft each. Installed prices use $12 to $25 per sq ft for 8 in. block, adjusted for the price difference of other block sizes, plus $2 to $8 per sq ft scaled to the share of cores filled. You can see every number in the cost breakdown.
Sources
- Quikrete Mortar Mix data sheet (blocks per bag)
- Inch Calculator: Cost to install a concrete block wall (installed and block prices, extras)
- Inch Calculator: Concrete block fill calculator (core fill volumes)
- HomeAdvisor: Cinder block wall cost (labor, block prices, permits)