How to calculate blocks for a wall
Blocks are counted by the face area of the wall. Each block, together with half of the mortar joint around it, covers a fixed area. Divide one square metre by that area to get blocks per square metre.
Blocks = net wall area × blocks per m² × (1 + wastage)
For a standard 400 × 200 mm block with a 10 mm joint: 1 ÷ (0.41 × 0.21) = 11.6 blocks per m². Always deduct doors, windows and other openings from the gross wall area first.
Worked example
A wall 24 m long and 3.2 m high has 76.8 m² gross. Deducting 6.5 m² of openings leaves 70.3 m². At 11.61 blocks per m² that is 816 blocks, or 858 once 5% wastage is added and rounded up.
Mortar, cement and sand
Mortar fills the joint space: the wall volume minus the volume of the blocks themselves. The dry volume of materials is about 1.33 times the wet mortar volume, split by the mix ratio. Cement is converted to mass at 1,440 kg/m³ and then to 50 kg bags.
Common block sizes in the UAE
| Thickness | Typical use | Blocks per m² |
|---|---|---|
| 100 mm | Internal partitions, shafts | 11.6 |
| 150 mm | Internal walls, light external | 11.6 |
| 200 mm | External walls, villas | 11.6 |
| 250 mm | Boundary and thermal walls | 11.6 |
Blocks per m² depend on the face size and joint, not the thickness. Thickness changes the mortar volume.
Frequently asked questions
How many blocks are in 1 m² of wall?
About 11.6 blocks of 400 × 200 mm with a 10 mm joint. Add 3–5% for breakage and cutting.
Should I deduct small openings?
Most measurement standards deduct openings above a minimum size, often 0.5 m². For quick estimates, deduct all doors and windows.
What mortar mix is used for blockwork?
1:5 or 1:6 cement to sand is common for general blockwork. Follow the project specification, which may call for 1:4 below ground or in load-bearing walls.