Quantities
Block quantity
- where
- blocks per square metre
- block length (mm)
- perpend joint (mm)
- block height (mm)
- bed joint (mm)
- net area (m²)
- waste allowance (%)
Explain this equation
This estimates how many blocks to order for an area of blockwork, including waste.
l and h are the block's face length and height in mm. j_p and j_b are the perpend and bed joints. Each block with its joints covers (l + j_p) × (h + j_b) of wall face, and N_m² is how many of those fit in one square metre. A is the net area and w the waste percentage.
There are 1 000 000 mm² in a square metre, so dividing by the face area of one block plus its joints gives the rate per m². A × N_m² is the net number, (1 + w/100) adds waste, and the ⌈ ⌉ brackets round up to whole blocks.
A 440 × 215 mm block with 10 mm joints covers 450 × 225 mm, about 9.9 blocks per m², usually taken as 10. Ten square metres with 5% waste needs 104 blocks.
Watch out: thin-joint systems use joints of only a few millimetres, so enter the manufacturer's figures rather than ordinary 10 mm joints.
Estimate blocks from the chosen face size and joint widths.
Enter your values to see the result.
Good to know
Example is a 440 × 215 mm block with 10 mm joints. Enter manufacturer values for thin-joint systems; do not assume ordinary mortar dimensions.
Sources
- Manufacturer sizes / geometry
Estimates are not design approval or British Standards compliance checks. Structural arch, retaining-wall, wind, foundation, lintel and masonry-capacity design are not performed. Use the project engineer’s specification.