Retaining Wall Block Calculator
How many blocks for a retaining wall
Building a retaining wall? Enter the wall length and finished height to estimate the number of standard retaining-wall blocks needed.
Estimating block count
Enter the wall length and finished height as your two dimensions. A standard block face is about 0.5 ft² (roughly 12" wide × 6" high), so plan on about 2 blocks per square foot of wall face.
Base course and burial
The most important course is the first one: set it on a compacted gravel base and bury it about one block-height below grade. A level, well-compacted base course is what keeps the whole wall straight for decades, so take your time getting it right before stacking higher.
Drainage makes or breaks it
Backfill behind the wall with free-draining gravel and add a perforated drain pipe at the base for taller walls. Water pressure behind a wall is the number-one reason blocks bulge and topple. Walls over about 3–4 feet usually need engineering and possibly geogrid reinforcement — check local codes.
Retaining Wall Block Calculator: frequently asked questions
How many retaining wall blocks per square foot?
About 2 standard blocks per square foot of wall face (12×6 inch face).
Do I need gravel behind a retaining wall?
Yes — free-draining gravel behind the wall prevents water pressure from pushing it over.
How tall can a retaining wall be without a permit?
Many areas allow DIY walls up to about 3–4 feet; taller walls typically require an engineered design, reinforcement and a permit. Always confirm the limit with your local building department.