Retaining Wall Calculator: Blocks, Base and Drainage Stone
Count the retaining wall blocks, caps, base gravel and drainage stone a wall needs from its length, height and block size, with cost. Enter the wall length and exposed height, pick the block, and get the courses including the buried one, the blocks and caps to buy, cubic yards and tons of base and drainage stone, the drain pipe and the cost.
Your numbers
From the finished grade in front of the wall to the top of the blocks, without the cap.
Allan Block buries 1 in for each foot of wall height. Leave empty to use that rule.
For breakage and the cut blocks at the ends and corners.
Leave empty to use the block length.
Allan Block: at least 24 in wide.
Compacted wall rock under the first course. Allan Block: at least 6 in.
Loose stone settles about 10% when it is compacted.
Allan Block: 12 in of wall rock behind the block, to the top of the wall.
Extra drain pipe from the end of the wall to where it can drain.
A driveway, parking, a building or a steep slope above the wall.
Wall blocks to buy
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- Courses
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- Built height
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- Blocks before spares
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- Wall face
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- Cap blocks
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- Base stone to order
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- Drainage stone
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- Drain pipe
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- Material cost
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Materials only. The wall's design, geogrid, footing and permit follow the block maker's instructions, your engineer and your local code.
The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.
How to use the retaining wall calculator
Enter the wall length and the height that will show above the finished grade, then pick the block or type its face size. The calculator adds the buried depth by Allan Block's rule of 1 in per foot of height, unless you type your own, and rounds up to whole courses. The trench, base and drainage figures start at Allan Block's minimums; change them to your block maker's.
Worked example: a 30 ft wall showing 3 ft, in 8 × 18 in blocks. 36 in plus 3 in buried is 39 in, so 5 courses of 20 blocks: 100, plus 5% is 105, with 21 caps. The base is 30 × 2 × 0.5 ft = 30 cubic feet, 1.22 cubic yards with compaction, about 1.73 tons. The drainage stone is 30 × 1 ft × 40 in built height = 100 cubic feet, 3.7 cubic yards, about 5.25 tons, and the drain pipe runs 30 ft plus the run to daylight.
What each number means
Courses are rows of block, counted from the buried one. Blocks per course are rounded up, because the last block in each row is cut to fit. The built height is the courses times the block height, which is usually a little more than the exposed height plus the buried depth; the drainage stone is figured to that height.
Base and drainage stone are in cubic yards and in tons, at a dry gravel density of 105 lb per cubic foot, about 1.42 tons per cubic yard. Crushed wall rock from your yard may weigh a little more or less, and their figure decides. Allan Block asks for wall rock, not sand, in the base, and a drain pipe at the back of the trench for walls over 4 ft, walls with poor drainage and every reinforced wall.
Retaining wall block sizes
Allan Block's AB Classic is 8 in high and 18 in long on the face, about 1 sq ft per block. The smaller blocks sold at home centers are smaller: Pavestone's RockWall Large is 6 × 17.5 in and the RockWall Small 4 × 11.75 in. Smaller blocks mean more courses and more pieces for the same wall, and the maker's guide gives the height a wall of them can reach without reinforcement.
For any other block, choose Custom face and type its height and length. Caps are counted by the wall length and the cap length; if your caps are a different length from the block, type it.
Pavers, gravel and block walls
A retaining wall often comes with a patio or a path at its foot or its top: the Paver Calculator counts the pavers, base and sand. The Gravel Calculator and the Cubic Yard Calculator work out stone and soil for any area and depth. For a mortared wall of concrete block, the Concrete Block Calculator counts the blocks, mortar and core grout.
For landscapers and hardscape crews
A wall quote rests on what was seen on site: the length and the height at each end, whether the grade steps, what sits above the wall, where the water runs and how the machine gets in. A missed step in the grade or a driveway nobody mentioned changes the block count, and can turn a gravity wall into an engineered one.
Sources, each read on 2026-10-24. All results are estimates; the block maker, your engineer and your supplier decide:
- Allan Block, Design Ideas 2025, Build an Allan Block Retaining Wall: trench 24 in wide and 6 in deep plus 1 in per ft of height; 12 in of wall rock behind the block; drain pipe for walls over 4 ft
- Allan Block AB Collection: AB Classic 8 in high × 18 in long, about 1 sq ft
- Pavestone RockWall Large, 6 × 17.5 in (Home Depot listing)
- Pavestone RockWall Small, 4 × 11.75 in (Home Depot listing)
- City of Grand Prairie, TX, residential retaining walls: the 2021 IRC text on 48 in of unbalanced fill and 24 in with other loads
- Engineering ToolBox, dirt and mud densities: dry gravel 105 lb/ft³
More for landscapers and home improvement pros: Landscaping sales, Home improvement sales, Quote follow-up email.
The wall is planned on the walk-through
The length, the height at each end, what sits above the wall and where the water goes all get said on site. Record the walk-through in ParrotNotes and get a transcript, a summary and the action items, so the quote is built from what was measured and agreed.
Get Started FreeRelated tools
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- Cubic Yard CalculatorWork out cubic yards of topsoil, mulch, gravel, sand or concrete for any area and depth, with tons, bags and cost, and convert yards to tons.Open the tool