How this calculator works
Subtract the cap height from total built height and round up the number of body courses. Each course rounds the unit count along the wall independently. The starting block face is 18 by 8 in (457.2 by 203.2 mm), corresponding to the cited Allan Block product family; replace dimensions with the actual supplied units. Gravel is a rectangular zone behind the wall, without a foundation pad, hollow cores or drainage pipe.
Formula
Courses = ceil((built height - cap height) / block height); blocks = ceil(courses x ceil(length / block width) x (1 + waste)); caps = ceil(ceil(length / cap width) x (1 + waste)); backfill V = backfill length x height x thickness.
Worked example
A 2 m long wall 0.8 m high using 400 by 200 mm block faces requires five blocks per course and four courses: 20 blocks before waste. A 0.3 m backfill zone holds 0.48 m3.
Advertisement
Frequently asked questions
Should I include buried blocks?
Yes. Enter the complete constructed height, including buried courses and the cap, rather than only the exposed wall height.
Does this check wall stability?
No. Soil pressure, surcharge, drainage, embedment, geogrid and allowable height require the manufacturer design method or an engineered plan.
Does the gravel include the base pad?
No. It covers only the specified rectangular backfill zone. Add the levelling pad and hollow-core fill separately.