Block wall calculator
This divides your wall's face by a block's face and rounds up. It does not judge whether a block wall suits the job, how it should be reinforced or bonded, or what it will bear — those are questions for your plans or an engineer. Confirm the count against the actual wall before you order.
Enter the wall's length and height and the face size of your block, and the tool works out the wall area, divides by the block's face area, adds a little for breakage and rounds up to whole blocks.
Ejemplo resuelto
A wall 20 ft long and 8 ft high is 160 ft². A standard block covers 16 × 8 inches, which is 128 in² or 0.889 ft², so 160 ÷ 0.889 = 180 blocks before waste. Add 5% for breakage and cuts and you would buy 189. A taller course count or a different block module shifts that straight away — the tool re-runs it as you edit.
In metric: a wall 6 m long and 2.4 m high is 14.4 m². A block laid at 400 × 200 mm covers 0.08 m², so 14.4 ÷ 0.08 = 180 blocks before waste; with 5% you would buy 189.
En la obra
A foundation, counted by the course. 28 ft × 40 ft, eight courses high. Centreline perimeter 136 ft = 1,632 in; at 16 in a block that is 102 blocks a course, × 8 = 816. Check it by area: 8 courses × 8 in = 64 in = 5.33 ft high, 136 × 5.33 = 725 ft², ÷ 0.889 = 816. Same answer both ways, which is the check you want before you order two pallets short. With 5%: 857 → 860 blocks, and the yard's pallet is a fixed count, so ask it and round to the pallet. In metric the course is the centreline perimeter ÷ 0.4 m: a 40 m perimeter is 100 blocks a course, eight 200 mm courses are 1.6 m high, and 40 × 1.6 = 64 m² ÷ 0.08 = 800 — the same answer both ways.
Corners and the half block. A running bond needs a half block at every other course on every corner and every end. Four corners × 8 courses is up to 32 halves — either cut on site (that is the waste) or ordered as half blocks. Either way the count of whole blocks does not drop; the 5% is what pays for the cuts and the one you drop off the scaffold.
A garden wall in 8 × 8 × 16 solids vs a retaining wall in a different module. Type the face of the block you are actually buying. A 12 in high architectural unit at 16 in long is 1.33 ft² a face — 75 blocks per 100 ft² instead of 112.5 (in metric, a 400 × 300 mm laid unit is 0.12 m² — 8.3 per m² instead of 12.5). The default is a starting point, not the answer.
What went wrong?
Quick referencefor block
- Standard block face, nominal
- 16 × 8 in = 0.889 ft² — 1.125 blocks per ft²
- Blocks per course
- wall length in inches ÷ 16 (¾ of a block per foot)
- Courses
- wall height in inches ÷ 8 (1½ per foot)
- Blocks per 100 ft² of wall
- 112.5 before waste · 118 at 5%
- Height by course
- 3 courses = 2 ft · 6 = 4 ft · 9 = 6 ft · 12 = 8 ft
- Metric block
- 390 × 190 mm block + 10 mm joint = 400 × 200 mm laid = 0.08 m² — 12.5 per m² (13.1 at 5%)
- Metric courses
- wall length ÷ 0.4 m a course (2.5 blocks per metre) · height ÷ 0.2 m (5 courses per metre)
Waste & overagewhat to add, and why
- Masons carry 5% on a plain wall and nearer 10% where there are corners, piers and openings — every half block is a cut, and cutting breaks a few. It goes in the waste field.
- Cubes of block come in fixed counts (often 90 or 96 per cube, but ask your yard); the buy line rounds to whole blocks, so round that up to whole cubes yourself if delivery is by the cube.
- Corner blocks, bond beams and half blocks are separate items on the ticket — count them from the plan and take them off the plain-block total rather than letting waste cover them.
Mistakes to catchbefore you order
- Typing the actual block size (15⅝ × 7⅝) instead of nominal (16 × 8): the joint is part of the module, and the actual size over-counts by about 7%.
- Measuring wall height to the top of the footing instead of the top of the finished course, or to the wrong side of a stepped footing.
- Counting a 40 ft wall with a 40 ft return as 80 ft of wall without dropping the overlap at the corner — the corner block serves both walls.
What an inspector looks forthe building inspector, in stages as the wall goes up
On this part of the job
- Bond and coursing: that the wall is laid to the pattern shown, that the courses are level, and that the height matches the drawing at each lift.
- Vertical steel in the cells the drawing calls for, held in position, with the lap where lengths meet — and that the cells are clean at the bottom so grout can reach.
- Grouted cells and bond beams done as shown and in lifts the code allows, with cleanouts where they are required.
- Anchorage: ties, straps, dowels and anchor bolts where the wall meets a floor, a roof or an adjoining wall.
- Mortar joints — tooled, full, and consistent. A wall with hollow head joints is a water problem and a strength problem at once.
Have this ready
- The wall elevation with the reinforcement and bond-beam layout.
- The mortar type the drawing specifies, and the bags to prove it.
- Cleanouts open and the cells swept before you call for the grout inspection.
Every figure an inspector measures against comes from the code your jurisdiction has adopted, the stamped drawing, or the manufacturer's printed instructions — so none of them are printed here. Look the number up in your own book, type it into the tool, and the arithmetic is yours.
La fórmula
blocks = (wall area × (1 + waste)) ÷ block face area, rounded up
Wall area is length × height. One block's face area is its nominal length times its nominal height, joint included, so the division already accounts for the mortar lines. The waste covers breakage and the part-blocks at ends and openings.
What this tool assumes
Only that a laid block covers its nominal face — and you set that face size, so even that is editable. The wall area, the block module and the waste are all yours; there is no hidden block table steering the count.
Preguntas
- How many concrete blocks do I need for a wall?
- Divide the wall face area by the face area of one block. A standard block laid up with its mortar joint covers about 16 inches by 8 inches, which is 128 square inches, or 0.889 ft² over its face — so a wall reads at 1.125 blocks per square foot. A metric block laid at 400 × 200 mm covers 0.08 m², which is 12.5 blocks per square metre. Enter your wall size above and the block count, plus a waste allowance, appears as you type.
- What size should I enter for the block?
- Use the nominal face size, mortar joint included — that is the area a laid block actually covers on the wall. A common CMU sits at 16 × 8 inches nominal (about 390 × 190 mm), which is the editable default here. A metric block is 390 × 190 mm itself and 400 × 200 mm laid with its 10 mm joint — the metric default. If your block is a different module, type its face length and height and the count follows.
- Do I subtract door and window openings?
- For a tight count, yes — measure the openings and knock their area off the wall area you enter. Many masons leave small openings in and let the waste factor absorb the cut blocks. For a big garage or window opening it is worth subtracting, since that is real blocks you would otherwise buy and stack for nothing.
- Does this include the mortar?
- No — this counts blocks only. Mortar is a separate order that depends on the joint size and the number of blocks, so it lives on its own page. Take the block count from here to the mortar calculator and it will turn it into bags.
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