Concrete Block Calculator
Work out how many concrete blocks a wall needs. The count uses the real 7⅝ × 15⅝ in block size, so 1.125 blocks fill each square foot, and openings and waste are handled for you.
- Actual block size, not nominal
- 4 to 12 in blocks and 440 mm blocks
- Courses, waste and cost
Concrete Block Calculator
Count the blocks for a wall
Width does not change the count. Every standard block shows the same 7⅝ × 15⅝ in face.
3/8 in in the US, 10 mm in the UK and Europe.
Results
Need the mortar for this wall? Get the bags, or the cement, lime and sand, in the Mortar Calculator.
Live wall preview
CMU wall——
How the count works
- Block area = wall area − openings = —
- One block plus its joint covers —
- Blocks per area = 1 ÷ that = —
- Blocks = block area × blocks per area = —
- Add wastage and round up = —
Courses = wall height ÷ (block height + joint). A height that is not a whole number of courses means cutting blocks or adjusting the joints.
What Is a Concrete Block Calculator?
A concrete block calculator is an online construction estimator that counts the concrete blocks in a wall from the wall length, wall height, block dimensions and mortar joint thickness. The same tool goes by 5 other names: block calculator, block wall calculator, concrete block estimator, cinder block calculator and concrete masonry unit (CMU) calculator.
The concrete block calculator measures the wall face. Every standard block shows a 15⅝ × 7⅝ in (397 × 194 mm) face, and with a 3/8 in (10 mm) mortar joint each block covers 16 × 8 in (406 × 203 mm) of wall. So the number of blocks needed depends on the square footage of the wall and the face of one block, not on the block width.
Our concrete block calculator has 5 working parts:
- Input fields take the wall length, wall height and every door and window.
- A block dimensions list holds standard 8 × 16 in blocks in all widths, half-high blocks, 440 × 215 mm metric blocks and a custom size.
- A mortar joint setting sets the joint thickness in inches or millimetres.
- A waste factor adds a percentage for broken and cut blocks.
- An output display shows the block area, blocks per square foot or square metre, the block count, the order quantity, the number of courses and the block cost.
How to Use the Concrete Block Calculator
To use the concrete block calculator, follow 6 steps. Results update as you type, and the Count Blocks button jumps to the full breakdown.
- Enter the wall length and wall height in feet, or switch to metric and enter metres.
- Add each door and window with its width, height and count. The calculator subtracts their area from the wall.
- Pick the block size. The standard option covers every 8 × 16 in block from 4 to 12 in wide.
- Leave the mortar joint at 3/8 in (10 mm in metric), unless the drawings call for another size.
- Keep the wastage allowance at 5%, or raise the figure for a wall with many cuts.
- Add the block price to see the concrete blocks cost.
The results panel gives 3 block numbers: blocks before wastage, which is the number of blocks in the finished wall, blocks to order with the wastage allowance, and the number of courses. Switch to metric to read blocks per square metre (m²) instead of blocks per square foot (sq ft).
Standard Concrete Block Sizes and Dimensions
The standard concrete block is the 8 × 8 × 16 in block, with an actual size of 7⅝ × 7⅝ × 15⅝ in (194 × 194 × 397 mm). Concrete blocks come in 5 common widths: 4, 6, 8, 10 and 12 in. All 5 widths share the same 8 × 16 in face, so all 5 need 112.5 blocks per 100 sq ft of wall. The chart showing the dimensions of standard blocks lists the nominal and actual sizes.
| Block (nominal W × H × L) | Actual size | Per sq ft | Per m² | Per 100 sq ft |
|---|---|---|---|---|
| 4 × 8 × 16 in | 3⅝ × 7⅝ × 15⅝ in (92 × 194 × 397 mm) | 1.125 | 12.1 | 112.5 |
| 6 × 8 × 16 in | 5⅝ × 7⅝ × 15⅝ in (143 × 194 × 397 mm) | 1.125 | 12.1 | 112.5 |
| 8 × 8 × 16 in | 7⅝ × 7⅝ × 15⅝ in (194 × 194 × 397 mm) | 1.125 | 12.1 | 112.5 |
| 10 × 8 × 16 in | 9⅝ × 7⅝ × 15⅝ in (244 × 194 × 397 mm) | 1.125 | 12.1 | 112.5 |
| 12 × 8 × 16 in | 11⅝ × 7⅝ × 15⅝ in (295 × 194 × 397 mm) | 1.125 | 12.1 | 112.5 |
| 8 × 8 × 8 in half block | 7⅝ × 7⅝ × 7⅝ in (194 × 194 × 194 mm) | 2.25 | 24.2 | 225 |
| 8 × 4 × 16 in half-high block | 7⅝ × 3⅝ × 15⅝ in (194 × 92 × 397 mm) | 2.25 | 24.2 | 225 |
| 440 × 215 mm metric block | 440 × 215 mm, 100 to 215 mm wide | 0.92 | 9.88 | 92 |
Assumptions: 3/8 in (9.5 mm) joints for US blocks and 10 mm joints for 440 × 215 mm blocks, single wythe, running bond, before wastage.
Nominal and actual block size. An 8 × 8 × 16 in block is a nominal size. The block itself is 3/8 in smaller each way, 7⅝ × 7⅝ × 15⅝ in, so that with a 3/8 in mortar joint the block fills exactly 8 × 16 in of wall. Dividing the wall by 8 × 16 in gives the right count. Treating 8 × 16 in as the block and then adding a joint undercounts by about 7%, or 7 to 8 blocks per 100 sq ft.
Block weight. Block weight sets how many blocks a truck, a pallet or a crew can move. The table lists typical dry weights for hollow concrete blocks; local mixes and moisture change the figures by a few pounds.
| Block | Typical weight |
|---|---|
| 4 × 8 × 16 in, normal weight | 20 to 25 lb (9 to 11 kg) |
| 8 × 8 × 16 in, normal weight | 35 to 45 lb (16 to 20 kg) |
| 8 × 8 × 16 in, lightweight | 25 to 30 lb (11 to 14 kg) |
| 12 × 8 × 16 in, normal weight | 50 to 60 lb (23 to 27 kg) |
Concrete Block Calculation Formula
The concrete block calculation formula divides the wall area by the area one block covers with its mortar joint. One standard block plus its joint covers 16 × 8 in, or 128 sq in (0.0826 m²), which is 0.889 sq ft.
Number of blocks = (L × H − openings) ÷ ((l + t) × (h + t))
Blocks to order = number of blocks × (1 + wastage %), rounded up
Courses = H ÷ (h + t)
The formula uses 5 values:
- L: length of the wall.
- H: height of the wall.
- l: actual length of one block, 15⅝ in (397 mm) for a standard block.
- h: actual height of one block, 7⅝ in (194 mm) for a standard block.
- t: mortar joint thickness, 3/8 in (10 mm) as standard.
Keep the units consistent. With the wall in feet and the block in inches, divide 144 sq in by the block cell: 144 ÷ (16 × 8) = 1.125 blocks per square foot. With the wall in metres and the block in millimetres, divide 1,000,000 mm² by the block cell: 1,000,000 ÷ (450 × 225) = 9.88 metric blocks per m².
Block course check. Each standard course rises 8 in (203 mm), so wall heights in multiples of 8 in need no cut blocks. An 8 ft (2.44 m) wall is 96 ÷ 8 = 12 courses, and each foot of wall length takes 0.75 blocks per course. Use the course height calculator for heights between courses.
Doors, Windows and Other Wall Openings
To count blocks for a wall with openings, subtract the area of every door and window from the wall area before multiplying by 1.125 blocks per square foot. The table shows the standard blocks that 6 common openings remove.
| Opening | Size | Area | Blocks saved |
|---|---|---|---|
| Single door | 3 ft × 6 ft 8 in (0.91 × 2.03 m) | 20 sq ft (1.86 m²) | 22.5 |
| Double door | 6 ft × 6 ft 8 in (1.83 × 2.03 m) | 40 sq ft (3.72 m²) | 45 |
| Window | 3 × 4 ft (0.91 × 1.22 m) | 12 sq ft (1.11 m²) | 13.5 |
| Small window | 2 × 3 ft (0.61 × 0.91 m) | 6 sq ft (0.56 m²) | 6.75 |
| Single garage door | 9 × 7 ft (2.74 × 2.13 m) | 63 sq ft (5.85 m²) | 70.9 |
| Double garage door | 16 × 7 ft (4.88 × 2.13 m) | 112 sq ft (10.41 m²) | 126 |
Do not add the opening area back to cover cut blocks at jambs. The wastage allowance covers those cuts. Openings in a load-bearing wall need 2 extra items:
- Lintel blocks (U-shaped bond-beam blocks) span the opening, and 8 in (200 mm) of bearing at each side is a common detail; follow the drawings. A 3 ft door needs (36 + 16) ÷ 16 = 3.25, so 4 lintel blocks per course of lintel.
- Jamb blocks with a finished end or a sash groove frame the sides of doors and windows, one per course at each side.
Block Wastage and Ordering Allowance
Order at least 5% more concrete blocks than the calculated number of blocks. The Concrete Masonry and Hardscapes Association (CMHA) works to 119 blocks per 100 sq ft in its estimating guide, TEK 4-2A, which is the 112.5 net figure plus 5%, rounded up. The table gives 4 typical waste percentages.
| Job | Wastage allowance |
|---|---|
| Straight wall, heights in multiples of 8 in | 5% |
| Wall with many openings, corners or pilasters | 8 to 10% |
| Short runs, curved walls or a lot of cutting | 10% |
| First block wall for a DIY builder | 10% |
Follow 3 rules for pallet quantity planning:
- Check the pallet count. A pallet of 8 × 8 × 16 in blocks holds 72 to 120 blocks, and 90 is a common count.
- Check the delivery weight. A pallet of 90 normal-weight 8 in blocks weighs about 3,150 to 4,050 lb (1.4 to 1.8 t).
- Order special units by name. Corner, half, lintel and bond-beam blocks come from the same total count, so list them on the order and reduce the standard blocks by the same number.
Concrete Block Calculation Example
A 30 × 8 ft (9.14 × 2.44 m) garage wall with one door needs 248 standard concrete blocks, and 260 blocks to order with 5% wastage. The table walks through each step.
| Step | Calculation | Result |
|---|---|---|
| Wall area | 30 ft × 8 ft | 240 sq ft (22.30 m²) |
| Door area | 3 ft × 6.67 ft | 20 sq ft (1.86 m²) |
| Block area | 240 − 20 | 220 sq ft (20.44 m²) |
| Block cell | (15⅝ + ⅜) × (7⅝ + ⅜) in | 128 sq in (0.0826 m²) |
| Blocks per sq ft | 144 ÷ 128 | 1.125 (12.1 per m²) |
| Number of blocks | 220 × 1.125 = 247.5, rounded up | 248 |
| Blocks to order | 247.5 × 1.05, rounded up | 260 |
| Courses | 96 in ÷ 8 in | 12 |
The same steps work for a 10 square meter wall. A 10 m² (107.6 sq ft) wall of US 8 × 16 in blocks takes 10 × 12.1 = 121.1 blocks, so 122 blocks and 128 to order with 5% wastage. The same wall in 440 × 215 mm metric blocks with 10 mm joints takes 98.8 blocks, so 99 blocks, and 104 blocks to order.
Concrete Block Cost Estimate
To estimate concrete blocks cost, multiply the blocks to order by the price per block. At an example price of $2.10 per block, the 260 blocks for the 30 × 8 ft wall cost 260 × $2.10 = $546.00, or about $2.48 per square foot of wall. Block prices change by region, block width and supplier, so use a local quote in the calculator.
Concrete blocks cost = blocks to order × price per block
Block cost per sq ft = price per block × 1.125 × (1 + wastage %)
A full block wall cost estimate has 6 parts, and the block calculator prices the first one:
- Blocks, including corner, half and lintel blocks.
- Mortar, as pre-mixed bags or as masonry cement and sand.
- Grout and rebar for reinforced or filled cores.
- Horizontal joint reinforcement, the ladder or truss wire laid in the bed joints.
- Delivery, often charged per pallet or per load.
- Labour, often the largest single cost on a contractor-built wall.
Mortar and Grout for Concrete Block Walls
One 80 lb (36 kg) bag of pre-mixed mortar lays 12 to 13 standard concrete blocks, which is the coverage QUIKRETE and SAKRETE publish for their bagged mortars. A 60 lb (27 kg) bag lays 9 to 10 blocks. For mixing on site, CMHA puts one 70 lb (32 kg) bag of masonry cement, mixed with sand, at about 30 hollow blocks, which works out at about 3.3 bags per 100 blocks. The Mortar Calculator works out the mortar volume, the bags and the cement, lime and sand split for the same wall, and the bag coverage guide compares the figures.
Grout fill. Grout fills the hollow cores of a concrete block wall around the rebar. A fully grouted 8 in wall takes about 1.12 cubic yards (0.86 m³) of grout per 100 sq ft, and a fully grouted 12 in wall about 1.65 to 1.75 cubic yards (1.26 to 1.34 m³). A wall grouted only at the reinforced cells, for example every 48 in (1.2 m), takes about one sixth of the fully grouted figure, plus any bond-beam courses.
Horizontal joint reinforcement. Ladder or truss reinforcement is laid in the bed joints, commonly every 16 in (406 mm), which is every second course. The length equals the wall length times the number of reinforced joints. The 30 × 8 ft wall has 96 ÷ 16 = 6 reinforced joints, so it takes 30 × 6 = 180 linear feet (55 m), or 18 pieces of 10 ft (3 m) plus the laps at the joins.
Use the concrete block calculator first to fix how many concrete blocks you need, then the Mortar Calculator for the mortar, cement and sand. Together the 2 estimates cover the blocks, the wastage allowance, the concrete blocks cost and the mortar for a concrete block wall. For a facing of clay bricks, the brick calculator counts the bricks for the same wall.
More Masonry Calculators
Each tool answers one question. Mortar volume, bags and the cement, lime and sand split live in the main Mortar Calculator.
Frequently Asked Questions
Are concrete blocks and cinder blocks the same?
No, concrete blocks and cinder blocks are not the same material, but stores sell both names for the same unit. True cinder blocks used coal cinders as aggregate and are rarely made today. A modern cinder block is a concrete masonry unit (CMU) with the same 8 × 16 in face, so a concrete block calculator gives the same count for both: 1.125 blocks per square foot.
How many concrete blocks come on a pallet?
A pallet of 8 × 8 × 16 in concrete blocks holds 72 to 120 blocks, and 90 is a common count. A pallet of 90 normal-weight blocks weighs about 3,150 to 4,050 lb (1.4 to 1.8 t). A 260-block order fills about 3 pallets of 90. Confirm the pallet count with the supplier, since the count changes with block width and plant.
Can I use this calculator for hollow and solid blocks?
Yes, the concrete block calculator works for hollow and solid blocks. The block count depends on the block face only, and hollow and solid blocks of the same size share the same face. Solid blocks weigh more and take no grout. For concrete hollow blocks (CHBs) with a 390 × 190 mm face, choose Custom size and enter 390 × 190 mm with a 10 mm joint, which gives 12.5 blocks per square metre.
Can I calculate concrete blocks for an L-shaped wall?
Yes, the concrete block calculator handles an L-shaped wall. Add the lengths of both legs measured along the outside face, subtract one wall thickness, 8 in (0.2 m) for 8 in block, for the shared corner, and enter the total as the wall length.
Do I need to order corner blocks and half blocks separately?
Yes, order corner blocks and half blocks by name, but count them inside the calculated total. A wall in running bond needs a block with a finished end on every course at each corner and free end, and a half block on every second course at each free end. A 12-course wall with 2 free ends needs 12 half blocks and 12 end blocks, which replace standard blocks in the same order.
Can I use this calculator for a retaining wall or foundation?
Yes, the concrete block calculator counts blocks for a CMU retaining wall or a block foundation stem wall. Include the courses below ground level down to the footing in the wall height. Reinforced retaining walls and foundations need grout and rebar to the engineer's design. Segmental retaining wall blocks, the dry-stacked interlocking type, have their own face sizes, so use the manufacturer's blocks per square foot or the Custom size option.
Why does my block estimate differ from my supplier's estimate?
There are 5 common reasons a block estimate differs from a supplier's estimate: a different waste percentage, a count based on the nominal 8 × 16 in size plus a joint, which reads about 7% low, rounding up to full pallets, special units such as corner, lintel and bond-beam blocks, and a wall height that is not a whole number of 8 in courses. Compare the wall area and the blocks per square foot behind both numbers first.