How many blocks a wall takes and how much bedding mortar goes with them. The answer comes out in purchase units — whole blocks and cubic metres of mortar — without breaking the mix down into cement and sand.
A hollow unit is bedded on its two outer shells only, about 55 % of the contact area. A solid unit takes a full bed.
| Gross wall area | 20.80 | m² |
|---|---|---|
| Net area, openings deducted | 18.70 | m² |
| Units per m² of wall | 11.4 | units/m² |
| Units before waste | 214 | units |
| Bedding mortar per m² | 0.0069 | m³/m² |
| Finished wall thickness | 15 | cm |
This is a theoretical figure based on joint area. It does not include mortar for filling cells or for levelling the first course; on a structural wall, add the grout for the reinforced cells separately.
Divide one square metre by the modular face of the unit: the block face plus one joint in each direction. A 40 × 20 cm block laid with a 12 mm joint covers 0.412 × 0.212 m, so a square metre takes about 11.5 blocks. Without any joint the same block would give 12.5, which is why quoting 12.5 always comes up short on site.
Bedding mortar fills the joint area left over once the block faces are subtracted, across the thickness of the wall. For a 15 cm hollow block with a 12 mm joint that is roughly 0.007 m³ per square metre of wall. Hollow units are bedded on their two outer shells only, so this calculator applies 55 % of the joint area to them and the full area to solid units.
Yes. The waste percentage is applied to both the block count and the mortar volume, and the block count is then rounded up to a whole unit. Five per cent suits a clean straight wall; raise it for short runs, many openings or a wall with a lot of cutting.
Because the volume of mortar is what you order or batch, and the mix design behind it changes with the specification, the sand and the supplier. Splitting one cubic metre into bags of cement and cubic metres of sand needs a mix ratio, which belongs in the unit-price analysis for the item, not in a quantity calculator.
These tools settle one quantity. Geztio builds the whole budget: chapters, unit-price analysis with real output rates, overhead and profit, and an Excel export.