Construction material calculator
Quantities for blockwork, plaster, reinforcing steel, floor tiles, paint and roofing sheets from your own dimensions. Every assumption is shown and can be changed. For concrete, use the concrete calculator.
Result
- Wall area, less openings
- 27 m²
- Blocks per square metre
- 11.61
- Blocks laid
- 313.6
- Blocks to buy, with waste
- 330
- Mortar (wet)
- 0.287 m³
- Cement for the mortar
- 76.7 kg
- Cement bags to buy
- 2 bags of 50 kg
- Sand for the mortar
- 0.32 m³
The mortar figure treats the blocks as solid. Hollow blocks laid on a full bed, or cores filled with mortar or concrete, take more.
No cost is estimated: the site has no verified material price observations yet, and it does not estimate a cost from an unverified figure.
What this is for
How many blocks a wall takes, and the cement and sand for the mortar that beds them. It is an estimate for ordering and checking, not a design or a bill of quantities for a contract.
How it works
- Wall area = length × height, less the doors and windows.
- One block with its joints covers (block length + joint) × (block height + joint); blocks per m² is one over that.
- Blocks to buy = area × blocks per m² × (1 + waste %), rounded up.
- Mortar is what the joints hold: area × wall thickness × (1 − block face ÷ face with joints).
- Dry mortar = wet mortar × the dry volume factor, split 1 part cement to the sand parts; cement weight = its volume × bulk density.
Assumptions
Each one is an input above. None of them is a legal or standard requirement.
| Assumption | Value used | Where it comes from |
|---|---|---|
| Block length | 0.4 m | Product size. Measure the blocks you will buy; hollow blocks of 400 by 200 mm on the face are common. |
| Block height | 0.2 m | Product size. |
| Wall thickness (block width) | 0.15 m | Product size. |
| Mortar joint | 0.01 m | Site rule of thumb. A 10 mm joint is the usual target for blockwork. |
| Waste allowance | 5 % | Site rule of thumb. Broken and cut blocks. Allow more for a wall with many openings. |
| Mortar mix, sand parts to one of cement | 6 | Your choice. 1 : 6 is a common mix for blockwork; the specification may call for a stronger one. |
| Dry volume factor for mortar | 1.3 | Site rule of thumb. Dry cement and sand take more room than the wet mortar they make; factors between about 1.27 and 1.33 are used on site. |
| Cement bulk density | 1440 kg/m³ | Material property. The loose bulk density of ordinary Portland cement, commonly taken as 1,440 kg per cubic metre for estimating. |
| Cement bag | 50 kg | Product size. Change this if your supplier sells a different bag. |
Worked example
A wall 10 m long and 3 m high with 3 m² of openings is 27 m². With 400 × 200 mm blocks and 10 mm joints each block covers 0.41 × 0.21 = 0.0861 m², so 11.6 blocks a square metre: 313.6 blocks, or 330 with 5% waste. The joints hold 0.287 m³ of mortar; at 1 : 6 and a factor of 1.3 that is 76.7 kg of cement (2 bags of 50 kg) and 0.320 m³ of sand.
Limitations
- The mortar figure treats blocks as solid; hollow blocks on a full bed, or filled cores, take more.
- Lintels, stiffening columns and bond beams are concrete work, not blockwork: use the concrete calculator.
- Quantities only: no labour, transport or cost.
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