How the mortar estimate is calculated
- Start with the number of blocks or bricks laid (not including spare units bought for breakage).
- Divide by the manufacturer's coverage: how many units one bag lays.
- Add your mortar waste allowance once, then round up to whole bags.
Example: 360 blocks at a stated 30 blocks per bag is 12 bags; with 10% waste that is 13.2, so buy 14 bags.
Why coverage must come from the bag
Two bags of the same weight can lay very different numbers of units, depending on the mix, the unit size, the joint width and whether the blocks are face-shell bedded. That is why this calculator never assumes a yield: it uses the figure the manufacturer publishes for the product you buy.
What this calculator does not cover
It estimates premixed bagged mortar only. Site-mixed mortar (cement, lime and sand by proportion) is a different calculation and is not included yet. Grout or concrete for filling block cores is separate: use the Block Fill Calculator.
Frequently asked questions
Should I use the block count including waste?
No. Waste blocks are spares for breakage and cuts; they are not laid with mortar. Use the laid count.
Where do I find bag coverage?
On the bag or the product data sheet, usually as the number of blocks or bricks laid per bag. If it isn't stated, ask your supplier.
This is a planning estimate based on the coverage you enter. Actual use depends on joint size, unit type, tooling and site conditions. It is not a supplier quotation.