Concrete Block & Wall Count Calculator
Count the 8×16 concrete blocks and the mortar bags for a wall from its length and height, with a waste allowance.
Calculator
A 20 × 8 ft wall (160 sq ft) takes about 190 standard 8×16 blocks and 6 bags of mortar. This is a block count/volume, not a retaining-wall design.
A concrete-block (CMU) wall is counted by area: a standard 8×16 block, mortar joint included, covers a known slice of wall face, so the block count is the wall area divided by that coverage. This tool does that and estimates the mortar bags too, with a waste allowance for cuts and breakage. It is a block count and material quantity only — never a retaining-wall or earth-pressure design, which is engineering work.
Formula
wall area = length × height
blocks = ceil(area ÷ 0.888 × (1 + waste%)) (0.888 sq ft per 8×16 block incl. joint)
mortar bags = ceil(blocks × 3 ÷ 100) (labeled ≈3 bags per 100 block)
Worked example
A 20 ft long × 8 ft tall wall with 5% waste:
- Area = 20 × 8 = 160 sq ft
- Blocks = ceil(160 ÷ 0.888 × 1.05) = ceil(189.2) = 190 blocks
- Mortar = ceil(190 × 3 ÷ 100) = 6 bags
Coverage, mortar & openings
The 0.888 sq ft per block figure is the standard nominal 8×16 face (7⅝×15⅝ in unit plus a ⅛ in joint) — a labeled typical, not a product spec, so confirm against your supplier’s unit. Subtract large door and window openings from the wall area before counting if you want a tighter number; the 5% waste covers cuts, breakage and the odd bad block. Mortar use varies with joint size and mixing, so treat ≈3 bags per 100 block as a planning figure and buy a spare bag. This tool stops at counting: sizing a load-bearing or retaining wall — rebar, grout cells, footings, drainage — is an engineer’s job.