How to use the concrete block calculator
- Enter the wall length and height. For several walls of the same height, add their lengths.
- Deduct doors and windows.
- Choose the block size. US blocks are listed by nominal size, which already includes the mortar joint.
- For US blocks, choose the block width and whether cores will be grouted to get the grout volume.
Block formula
Blocks = Wall area ÷ Block face area (including one joint) 8 × 16 in block: 0.889 ft² → 1.125 blocks per ft² 400 × 200 mm: 0.08 m² → 12.5 blocks per m² Mortar ≈ 3 bags per 100 blocks · Grout (8 in block) ≈ 0.25 ft³ per block
Worked example
A garage wall 40 ft long and 8 ft high with standard 8 × 8 × 16 blocks, cores fully grouted:
- Area = 320 ft² × 1.125 = 360 blocks; with 5% extra = 378
- Mortar ≈ 378 × 3 ÷ 100 = 11.3 → 12 bags
- Grout = 360 × 0.25 ft³ = 90 ft³ = 3.33 yd³
Block sizes and coverage
| Block | Face (with joint) | Blocks per ft² / m² |
|---|---|---|
| US 8 × 8 × 16 in (CMU) | 8 × 16 in | 1.125 per ft² |
| US 4 × 16 in half-high | 4 × 16 in | 2.25 per ft² |
| Metric 390 × 190 mm | 400 × 200 mm | 12.5 per m² |
| Metric 440 × 215 mm (UK) | 450 × 225 mm | 9.88 per m² |
| AAC 600 × 200 mm | 600 × 200 mm | 8.33 per m² |
Core grout per block (fully grouted)
| Block width | ft³ per block | Blocks per yd³ of grout |
|---|---|---|
| 6 in | 0.17 | ≈ 159 |
| 8 in | 0.25 | 108 |
| 10 in | 0.33 | ≈ 82 |
| 12 in | 0.39 | ≈ 69 |
Hollow, solid and AAC blocks
Hollow concrete blocks are light, quick to lay and let you run steel and grout through the cores. Solid concrete blocks are heavier and used for load-bearing walls and boundary walls in many countries, including India. AAC (autoclaved aerated concrete) blocks are very light, insulate well and are laid with thin adhesive, so they need far less mortar and are popular for partition and infill walls in RCC-frame buildings. Whatever the type, count blocks the same way — by face area — and check the supplier’s exact size.
Tips for block walls
- Plan to the module. Make wall lengths multiples of 8 in (or 200 mm) and heights multiples of 8 in to avoid cutting blocks.
- Footings first. Block walls need a level concrete footing, usually twice the wall’s width.
- Reinforce where needed. Retaining walls, basements and walls in seismic or high-wind zones need rebar in grouted cores and horizontal joint reinforcement — follow your engineer and local code.
- AAC blocks use thin-bed adhesive instead of thick mortar; check the manufacturer’s coverage per bag.
- Keep blocks dry before laying and cure mortar and grout properly.
- Order by the pallet if you can — suppliers often discount full pallets.