Retaining Wall Calculator
This retaining wall calculator finds how many blocks a wall needs from its length, height, and block size. Enter them with a waste allowance and the retaining wall calculator returns the block count, the number of courses, and the wall face area. As a retaining wall block calculator it sizes segmental block walls for gardens, terraces, and driveways.
Results
The Retaining Wall Calculator is part of our Structural collection. Browse more structural to size, convert, and check your work alongside this tool.
What the retaining wall calculator shows
A block retaining wall is built up in courses, and the retaining wall calculator works out how many blocks that takes. It finds the wall face area from the length and height, divides by the face area of one block, adds a waste allowance for cuts, and rounds up. As a retaining wall block estimator it also shows the number of courses, so you can plan the base and the cap.
How the retaining wall block calculator counts blocks
The retaining wall block calculator divides the wall face area by the block face area, adds waste, and rounds up:
The face area sets the block count, while the height divided by the block height gives the courses, the horizontal rows. This retaining wall block estimator rounds up both, since you buy whole blocks and build whole courses.
Retaining wall calculator example
A wall 10 m long and 1.2 m high, using 400 by 200 mm blocks, with 10 percent waste. The retaining wall calculator gives:
So the wall needs 165 blocks in 6 courses. Change the height and the retaining wall calculator updates the count at once.
How to use the retaining wall calculator
Enter the wall length and height in meters, the block length and height in millimeters, and a waste allowance, then the retaining wall calculator returns the blocks, the courses, and the face area. Use the exposed face size of your block. A 10 percent waste allowance covers cuts at ends and corners, which a retaining wall block calculator needs since walls rarely land on a whole block.
Reading the retaining wall block estimator result
The block count is how many units to order, with waste and rounding built in; the courses tell you how many rows to lay. A retaining wall also needs a compacted base, a levelling pad, drainage gravel behind it, and often a concrete footing for taller walls, none of which the block count covers. Check local rules, since walls above about a meter often need engineering. The retaining wall block estimator gives the blocks and courses; add the base, backfill, and cap separately.
When to use the retaining wall calculator
- Ordering blocks for a garden wall with the retaining wall calculator
- Planning courses for a terrace with a retaining wall block calculator
- Pricing a job with a retaining wall estimate
- Comparing block sizes for a driveway wall
Common retaining wall calculator mistakes
- Using overall block size for the face. Enter the exposed face length and height, not the full depth.
- Skipping the base and backfill. The block count ignores gravel and footing, so size those separately.
- Ignoring engineering. Walls above about a meter often need a designed footing and drainage.
Tips for retaining walls
- Level and compact the base course carefully; it sets the whole wall.
- Add drainage gravel behind the wall to relieve water pressure.
- Order 10 percent extra for cuts at ends and corners.
Concrete retaining wall calculator and footing
Blocks are only the visible part of a retaining wall, and a concrete retaining wall calculator handles what sits under and behind them. Most segmental walls start on a compacted gravel base with a levelling pad, but taller or heavily loaded walls need a concrete footing to spread the load and stop the wall tipping. To size that footing, treat it as a strip and find its volume from length, width, and depth, which is where a concrete calculator for retaining wall work comes in. Poured concrete retaining walls, as opposed to block ones, replace the block count entirely with a concrete volume, so a retaining wall concrete calculator there works from the wall thickness, height, and length instead. Match the method to the wall type before you order.
Retaining wall block estimator by course
Thinking in courses helps a retaining wall block estimator make sense on site. The first course is the most important, since it sets the line and level for everything above, so builders bed it carefully on the levelling pad. Each course above steps back slightly for batter, the backward lean that helps the wall resist the soil, and many systems interlock or pin the courses together. Because the count comes from the face area, a taller wall of the same length needs proportionally more blocks and more courses, and it also needs more drainage gravel behind it to relieve water pressure. For the base and backfill, the gravel calculator sizes the stone the wall depends on, while this tool gives the blocks and rows.
Retaining wall block calculator reference
Blocks per square meter of wall face by block size, for the retaining wall block calculator, before waste:
| Block face size | Block face area | Blocks per m² |
|---|---|---|
| 400 × 200 mm | 0.08 m² | 12.5 |
| 300 × 200 mm | 0.06 m² | 16.7 |
| 450 × 150 mm | 0.0675 m² | 14.8 |
| 600 × 200 mm | 0.12 m² | 8.3 |
Retaining Wall Calculator FAQ
How does the retaining wall calculator count blocks?
It divides the wall face area by one block face area, adds waste, and rounds up. The retaining wall calculator also gives the number of courses from the height.
What is a course?
A course is one horizontal row of blocks. The retaining wall block estimator finds the courses by dividing the wall height by the block height and rounding up.
Do I need concrete for a retaining wall?
Often yes. Taller walls need a concrete footing, so a concrete retaining wall calculator sizes that base separately from the block count.
What else does a wall need?
A compacted base, a levelling pad, drainage gravel behind the wall, and sometimes engineering above about a meter. The block count does not include these.