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Block calculator: how many blocks for an internal wall?
Estimate blocks, lintels, sand and cement for internal block walls. Enter the wall length and height, choose the block type and thickness, and add any door openings.
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How the calculation works
A standard concrete or aerated block face is 440 × 215 mm, so with mortar joints you need about 10 blocks per square metre of wall. The calculator takes the wall area, removes door openings, and adds your waste allowance.
Each opening needs a lintel, and the mortar is converted into sand and cement bags for you.
Choosing a block
Aerated blocks are light and quick to lay and cut, and suit most internal partitions. Medium dense and dense concrete blocks are heavier and stronger, and are chosen where a wall carries load or needs better sound insulation.
100 mm blocks are the usual choice for partitions; 140 mm gives a stiffer wall and better sound performance.
Worked example
A 4 m long, 2.4 m high internal wall in 100 mm aerated blocks with one door opening:
| Material | Quantity | Price (ex VAT) |
|---|---|---|
| 100mm Thermalite Shield Block 3.6N | 91 | £183.82 |
| Supreme Concrete Prestressed Textured Concrete Lintel 65mm x 100mm x 1200mm P100 | 1 | £15.09 |
| Soft Building Sand 25kg Bag | Ideal for Bricklaying & Mortar | 4 | £15.20 |
| Blue Circle Mastercrete Grey Cement in Plastic Bag 25kg | 2 | £15.34 |
| Materials total | £229.45 | |
Today's prices, excluding VAT and delivery. Labour, plant hire and some items are priced when you request a quote. Use the calculator above for your own measurements.
Frequently asked questions
How many blocks per square metre?
About 10 standard 440 × 215 mm blocks per square metre, before waste.
Do I need a lintel over an internal door?
Yes, an opening in a block wall needs a lintel to carry the blocks above it. The calculator adds one for each door you enter.
Aerated or concrete blocks for an internal wall?
Aerated blocks are lighter and easier to work for most partitions. Choose dense or medium dense blocks for load-bearing walls or where sound insulation matters more.