Walls over 4 ft usually need an engineer and a permit.
Used to size the gravel base behind and below the wall.
Covers cuts at corners and the odd cracked block.
An estimate, not an engineering design. Retaining walls hold back soil and water, and failures are expensive and dangerous. Anything above 4 ft, or any wall holding a slope or a driveway, needs a qualified engineer and almost certainly a permit.
Calculated entirely in your browser. Nothing you enter is sent anywhere.
How to use it
Measure the wall
Total length and finished height above ground, in feet.
Measure one block
Length, height and depth in inches, printed on the pallet or the supplier page.
Remember the buried course
Roughly one tenth of the wall height sits below grade. The result accounts for it.
How the calculation works
Blocks per course is wall length divided by block length, rounded up. Courses is wall height divided by block height, also rounded up. Multiply, add waste for cuts at corners, and that is your count.
Cap blocks are counted separately because they are a different product at a different price. You need one course along the top.
The gravel covers two things. A compacted base below the wall, roughly twice the block depth wide and six inches deep, which spreads the load. And drainage stone behind the wall, which stops water pressure building and pushing it over. Of the two, the drainage stone is the one people skip and the one that causes failures.
What this calculator does not do
This is not an engineering design. Retaining walls hold back soil and water, and a failure is dangerous as well as expensive.
Anything above four feet, or any wall supporting a slope, a driveway or a structure, needs a qualified engineer and almost certainly a permit.
It does not account for geogrid reinforcement, which taller walls need through the backfill, nor for stepping the base on sloping ground.
Questions
How tall without an engineer?
Usually four feet, but the limit varies and some areas set it lower. Check locally before you buy anything.
Why bury the first course?
Burying roughly one tenth of the height anchors the base against soil pressure pushing outward. Skipping it is the most common cause of failure.
Do I need gravel behind it?
Yes. Water trapped behind a wall creates enormous pressure. Drainage stone and a perforated pipe let it escape.
What is setback?
Each course sits slightly back from the one below, usually built into the block by a lip. It leans the wall into the slope rather than away.
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