Block Calculator - CMU Count, Mortar Bags & Wall Cost
Block count is wall area minus openings, multiplied by the selected block coverage. Add waste for cuts and breakage, then estimate mortar bags and cost.
Percent added for cuts, waste, settlement, or field loss.
Cost uses the waste-adjusted block count.
Change any value and the results, formula, and diagram update immediately. Use the same unit system throughout one estimate.
Blocks Per Square Foot - Quick Reference
These are the block counts per face area for the most common CMU sizes, running bond, 3/8 inch / 10 mm mortar joint. Multiply by your net wall area for the on-site sanity check; the calculator above handles your exact block size and openings.
| Block size | Region | Nominal (with joint) | Per sq ft | Per sq m |
|---|---|---|---|---|
| 8 x 8 x 16 in CMU | US standard | 8 x 16 in face | 1.125 | 12.1 |
| 6 x 8 x 16 in CMU | US narrow | 8 x 16 in face | 1.125 | 12.1 |
| 4 x 8 x 16 in CMU | US partition | 8 x 16 in face | 1.125 | 12.1 |
| 8 x 4 x 16 in CMU (half-high) | US accent | 4 x 16 in face | 2.25 | 24.2 |
| 440 x 215 mm block | UK / Europe | 450 x 225 mm face | 0.92 | 9.88 |
| 390 x 190 mm block | India (modular) | 400 x 200 mm face | 1.16 | 12.5 |
| 625 x 250 mm AAC block | India / SE Asia AAC | 635 x 260 mm face | 0.55 | 5.92 |
| 390 x 190 mm CMU | Australia / NZ | 400 x 200 mm face | 1.16 | 12.5 |
Face area is what the wall shows. Wall thickness (6 in vs 8 in vs 12 in) does not change the face count - it changes the block weight, grout cells, and how much reinforcement the wall can carry.
Why "1.125 Blocks Per Square Foot" Is The Magic Number
A standard US concrete masonry unit (CMU) is 7-5/8 x 7-5/8 x 15-5/8 inches. Add a 3/8 inch mortar joint on every side and the estimating module is 8 x 16 inches, or 128 square inches. A square foot is 144 sq in, so 144 / 128 = 1.125 blocks per sq ft of face. That is the number every mason and estimator memorizes.
The same logic gives 12.1 blocks per square metre. Wider joints (1/2 in) drop the count slightly. Custom block sizes (split-face, half-high, scored) change the face area and therefore the count. The calculator uses your actual block face and joint - if you do not change anything, it defaults to the US standard 8 x 16.
Block Sizes Around The World
United States (ASTM C90)
Hollow CMU at 8 x 8 x 16 in nominal is the workhorse. 6 in and 12 in widths follow the same 8 x 16 face. Lightweight (under 105 pcf), medium-weight, and normal-weight blocks differ on density but not face count.
United Kingdom (BS EN 771-3)
Standard block is 440 x 215 mm face with widths from 100 mm (partition) to 215 mm (load-bearing). Dense, medium-dense, and aircrete (Celcon, Thermalite) are the common pours. Aircrete is light enough to lay one-handed.
India (IS 2185, IS 6041)
Solid and hollow CMU sit at 400 x 200 mm face. AAC blocks (Birla Aerocon, Magicrete, Siporex) are 600-625 mm long x 200-250 mm tall - lighter and faster to lay than CMU, now the default in urban Indian construction.
Australia / New Zealand
390 x 190 mm face with 90, 140, 190, and 290 mm widths. Hollow grey block dominates; coloured and split-face go on visible walls. Same face count as Indian metric block.
Europe (Eurocode 6)
Sizes vary by member state. Belgium and Netherlands tend to 390 x 190 mm; Germany uses Kalksandstein at 240 x 113 mm or 248 x 248 mm; Poland and the Nordics often use aircrete in 600 mm lengths.
Mexico & Philippines
Mexico's tabicon and block hueco sit close to 200 x 200 x 400 mm. The Philippines uses CHB - concrete hollow block - in 4 in, 6 in, and 8 in widths at 8 x 16 in face. Both markets often use cement-poor mixes; check delivered weight against the spec.
Hollow, Solid, Grouted - Which To Order
The block face count does not change with block weight, but the wall behaviour and price absolutely do.
- Hollow block is the residential default. About 28-38 lb (13-17 kg) per 8 in CMU. The cells stay empty unless you grout them.
- Solid block is one continuous web; about 50-60 lb (23-27 kg) per 8 in unit. Used for bond beams, lintels, and where fire rating is critical.
- Partially grouted walls have grout only in the cells that hold vertical rebar (typically every 32-48 inches). The block count is unchanged; the grout count is separate.
- Fully grouted walls fill every cell. Adds about 0.013 yd³ (0.01 m³) of grout per 8 in block. This is normal for retaining walls, basement walls, and any wall carrying significant load.
- Aircrete / AAC blocks are very light (about 25-35% of CMU weight) but only suit non-load-bearing or low-load walls. Cut with a hand saw, lay with thin-bed adhesive instead of standard mortar.
Reinforcement and Bond Beams
Code-driven block walls almost always carry steel. The calculator does not size rebar - use the Rebar Calculator for that - but here is what to expect on a permitted residential wall:
- Vertical rebar in grouted cells, usually #4 or #5 at 32 to 48 in on centre, more for tall walls or seismic zones.
- Horizontal joint reinforcement (truss-type ladur wire or rebar in bond beam blocks) every 16 in.
- Bond beam at the top of the wall and over openings - a solid-block course with horizontal rebar inside.
- Dowels into footing matching vertical bar size, with a lap length of 40 bar diameters.
Indian construction often uses tor-steel or TMT bars at similar spacing; UK domestic walls rely on bed-joint reinforcement strips (Brickforce, Bricktor) instead of rebar in cells.
Mortar - About 3 Bags Per 100 Blocks
For US 8 x 8 x 16 CMU with 3/8 in mortar joints, plan about 3 bags of pre-mixed mortar (70 lb) per 100 blocks. UK practice uses about 1 m³ of mortar per 1,000 blocks for solid walls. India works to roughly 0.025 m³ mortar per m² of 200 mm wall at 1:6 cement-sand ratio.
Mortar volume swings with workmanship - sloppy joints waste material on the board, tight joints save it. For grouted walls the grout is a separate order, not a mortar count. The calculator gives a planning bag count; use the Mortar Calculator for a precise per-joint takeoff.
Cost Estimates Around The World
2026 retail planning prices for a standard hollow concrete block (US 8 x 8 x 16, or local metric equivalent). Decorative, split-face, coloured, fluted, and architectural blocks cost 2-4x more.
| Region | Standard hollow block | Solid block | Mason day rate |
|---|---|---|---|
| United States (USD) | $1.30-2.50 each | $2.50-4.50 each | $320-550 / day |
| Canada (CAD) | C$1.80-3.20 each | C$3.20-5.50 each | C$400-650 / day |
| United Kingdom (GBP) | £1.30-2.50 each | £2.20-4.00 each | £200-320 / day |
| Eurozone (EUR) | €1.20-2.40 each | €2.10-4.20 each | €220-360 / day |
| Australia (AUD) | A$2.50-4.50 each | A$4.50-7.50 each | A$450-700 / day |
| India (INR) | ₹35-55 each (CMU) | ₹55-90 each | ₹800-1,500 / day (mason + helper) |
| India (INR) - AAC blocks | ₹40-80 each (625x250x150 mm) | n/a | same labour |
| Mexico (MXN) | MX$20-40 each | MX$45-75 each | MX$500-900 / day |
| Philippines (PHP) | PHP 15-25 each (CHB) | PHP 30-50 each | PHP 600-1,200 / day |
A working mason lays 200-400 standard blocks per day on straight running bond wall. Cuts, corners, openings, and bond beams drop that to 100-200. AAC blocks lay much faster - 300-500 per day - because they are lighter and the thin-bed glue is faster than mortar.
Common Mistakes
- Counting gross wall area without subtracting doors, windows, and large vents.
- Using the nominal 8 x 16 face on a block that is actually metric 400 x 200 mm.
- Forgetting that bond-beam courses use solid blocks, not hollow.
- Skipping the grout estimate on a load-bearing or basement wall.
- Using CMU mortar volume for AAC blocks - AAC uses thin-bed adhesive, a much smaller quantity.
- Mixing 6 in and 8 in widths on a single wall without coordinating the bond.
- Treating block face count as block weight - a hollow block weighs about half what a solid block does.
- Ordering exact counts; blocks ship on pallets in 50 to 200 unit cubes and partial pallets cost more per block.
Block Calculator FAQ
How many blocks do I need for a 20 x 8 ft wall?
A 20 x 8 ft wall is 160 sq ft. At 1.125 blocks per sq ft, that is 180 blocks for the face. Add 10% waste and you order 198 - call it 200. For Indian metric block (400 x 200 mm at 12.5 per m²), 160 sq ft is 14.86 m², so 186 blocks before waste.
What is the difference between hollow and solid block?
Hollow blocks have one or two large cells running top to bottom. They are lighter, cheaper, and let you run rebar and grout through the cells. Solid blocks are one continuous web - heavier, more expensive, used where you need a full bond beam, fire rating, or a lintel.
How many mortar bags per 100 blocks?
About 3 bags of pre-mixed mortar (70 or 80 lb) per 100 standard 8 in CMU. For thin-bed AAC adhesive, plan about 1 bag of glue per 4-5 m² of wall - much less material than CMU mortar.
How much does a concrete block weigh?
A standard 8 x 8 x 16 in hollow CMU weighs 28-38 lb (13-17 kg). A solid block of the same size is 50-60 lb. A 200 mm Indian AAC block weighs 8-10 kg - light enough to lay with one hand. Block weight is why aircrete and AAC have taken over urban Indian residential construction.
Do I need rebar in a concrete block wall?
Above garden-wall height, almost always yes. Residential walls typically use #4 or #5 vertical rebar at 32-48 in on centre with horizontal joint reinforcement every 16 in. Code requirements get stricter in seismic and high-wind zones. Single-storey freestanding walls under 3 ft can sometimes skip rebar; basement and load-bearing walls cannot.
Should I use AAC or concrete block?
For non-load-bearing partition walls, AAC is faster, lighter, and gives better thermal insulation. For load-bearing exterior walls, retaining walls, basement walls, or anywhere with grouted rebar, traditional CMU is the safer call. India and Southeast Asia have largely shifted residential interiors to AAC; perimeter walls remain CMU or brick.
What waste factor should I use?
Straight walls: 5-8%. Walls with corners, half blocks, returns, or openings: 10-12%. Heavily reinforced or repair walls: 12-15%. The waste covers cuts, breakage, and the units the mason rejects for chips.
How do I calculate the mortar between blocks?
For a 1,000 sq ft wall of 8 x 16 face block: that is 1,125 blocks. At 3 bags per 100 blocks, you need about 34 bags of mortar. Joint thickness and profile (concave vs flush vs raked) shift this 10-15% either way. Use the dedicated mortar calculator for a precise number.
Why is my supplier quoting a different block count?
Suppliers may use a slightly different nominal face (some 7-5/8 vs 8 vs metric 390 mm), a different joint assumption, or a coverage value with built-in waste. Ask the supplier which face dimension and which joint thickness they used; that explains 95% of the discrepancy.
How tall can a block wall go without engineering?
Most US codes let unreinforced freestanding walls go to about 6 ft (1.8 m) before they need rebar and engineering review. Retaining walls over 4 ft (1.2 m) - or any height with surcharge load - require engineered design. UK garden walls follow BS EN 1996 thickness tables. Indian residential boundary walls are usually 2-2.4 m on 230 mm thick brick or block with intermediate piers.
Related Construction Calculators
For mortar bags and the cement-sand mix, see the Mortar Calculator. For clay brick walls switch to the Brick Calculator. Reinforcement in grouted cells uses the Rebar Calculator. Footings under the wall start in the Footing Calculator and the Concrete Calculator. More tools live on the Construction Calculators hub.
Sources
- Concrete Masonry & Hardscapes Association (CMHA) resources
- ASTM C90 standard specification for loadbearing concrete masonry units
- The Masonry Society - TMS 402/602 standards
- UK Brick Development Association (covers concrete block too)
- Bureau of Indian Standards - IS 2185, IS 6041, IS 2572 block masonry codes
- NIST Handbook 44 unit conversion tables
This calculator is for planning and ordering conversations. Local code, project drawings, engineered design, and manufacturer instructions control the final work.