Method and guidance
How to use the retaining wall materials calculator
- Enter the length and exposed height of one straight wall segment. Curves, corners, steps, and returns need a project-specific takeoff.
- Enter the installed face length and course height of the exact standard block. The calculator rounds exposed height up to whole courses.
- Enter the whole buried-course count required by the design, an explicit block-and-cap waste allowance, and any known additional standard blocks.
- Optionally enter cap face length. Cap demand uses wall length and the same visible waste allowance, then rounds to whole caps.
- Enter the specified aggregate-base width and compacted depth plus the behind-wall drainage-zone width. These create visible rectangular quantity prisms.
- Optionally price standard blocks, caps, and combined aggregate. Review exact demands, whole-unit purchasing, and the partial cost separately.
Formula and calculation order
All lengths normalize to meters. Course and purchase ceilings occur only at their documented boundaries.
above-grade courses = round up(exposed height ÷ block course height)
total courses = above-grade courses + entered buried courses
modeled total height = total courses × block course height
exact blocks per course = wall length ÷ block face length
exact standard blocks = exact blocks per course × total courses
adjusted standard blocks = exact blocks × (1 + waste ÷ 100) + additional blocks
whole standard blocks = round adjusted standard blocks up once
exact caps = wall length ÷ cap face length
adjusted caps = exact caps × (1 + waste ÷ 100)
base volume = wall length × base width × base depth
drainage volume = wall length × drainage width × modeled total height
aggregate order volume = (base volume + drainage volume) × (1 + overage ÷ 100)Standard-block and cap costs use whole units. Aggregate cost uses exact order volume converted to the selected bulk price unit. The total includes only components whose prices were supplied.
Independently verified worked example
A 20 ft wall with 2 ft exposed height and a 6 in course height requires exactly four exposed courses. One entered buried course produces five total courses and 2.5 ft of modeled total height.
A 16 in face length gives 15 exact blocks per course and 75 exact standard blocks before waste. Five percent adds 3.75 blocks; with no explicit additional units, adjusted demand is 78.75 and purchase quantity rounds once to 79 blocks.
A 12 in cap length gives 20 exact caps. Five percent adds one cap, so 21 whole caps are required.
A 24 in wide by 6 in deep base along 20 ft uses 20 ft³. A 12 in wide drainage prism along the 2.5 ft modeled total height uses 50 ft³. Combined design volume is 70 ft³; 10% order overage produces 77 ft³, or 2.851851… yd³.
At $4 per standard block, $5 per cap, and $55/yd³ for aggregate, the component costs are $316, $105, and $156.851851…; their partial total is $577.851851… before display rounding.
Material guidance and source boundaries
Allan Block's material-estimation worksheet calculates blocks from wall length, block width, total height including buried block, and block height; it recommends adding 5% for waste and emphasizes exact product dimensions. Review the Allan Block estimation worksheet (manufacturer estimating reference).
Allan Block's basic installation guidance treats base preparation, buried block, wall rock, drain pipe, backfill, and compaction as related but distinct construction steps. Review basic retaining-wall installation guidance (manufacturer installation reference).
The Allan Block residential guide describes a typical wall-rock zone behind the block and repeatedly directs users to approved plans and site-specific requirements, especially for reinforced walls. Review the residential retaining-wall guide (manufacturer guide PDF).
Allan Block does not sponsor Calculate My Project. These references establish estimating boundaries, not a universal design for every block system or site.
Common estimating mistakes
- Dividing entered height by nominal block height but failing to round up to a buildable whole course.
- Omitting buried courses from both block count and the height of behind-wall aggregate.
- Using overall block depth or pallet dimensions instead of installed face length and course height.
- Rounding blocks per course, every course, waste, and final purchase independently without documenting the multiple ceilings.
- Treating standard blocks as though they include corners, ends, steps, curves, specialty units, reinforcement, or caps.
- Applying a generic aggregate volume without making base and behind-wall drainage geometry visible.
Limitations
Version 1 models one straight segmental wall with one standard block face and optional cap face. It does not model curves, corners, ends, returns, steps, tiers, batter, setback, varying grade, openings, columns, or specialty units.
Base and drainage quantities are full rectangular prisms. They do not subtract block embedment or account for drain pipe, grading, compaction change, excavation tolerance, geotextile, native backfill, topsoil, caps, or shape-specific manufacturer details.
The calculator does not assess global, sliding, overturning, bearing, settlement, internal, compound, seismic, water, surcharge, slope, fence, guard, or tiered-wall stability. It does not determine geogrid type, length, elevation, or coverage.
Wall height, loading, soil, groundwater, utilities, property boundaries, local code, and permit rules can require a licensed design professional and approved plans. Cost excludes unpriced materials, delivery, tax, excavation, disposal, drainage pipe, fabric, adhesive, reinforcement, tools, labor, engineering, and permits.
Frequently asked questions
Why can modeled exposed height exceed the entered height?
Segmental walls use whole courses. The calculator rounds exposed height up to the first whole course that reaches it and shows both values.
Does five percent waste automatically apply?
The form starts at 5% as visible manufacturer-aligned planning guidance. You can edit it, and the submitted value is shown in results. It applies to standard blocks and optional caps.
What are additional standard blocks for?
They let you add a known whole-unit quantity separately from percentage waste. They do not automatically identify corner, end, step, cut, or specialty units.
Why does drainage volume use modeled total height?
The quantity prism extends along the entered behind-wall width and the course-based height including buried courses. Actual drainage-rock limits must follow the approved design and product system.
Does this calculator tell me whether geogrid is required?
No. Reinforcement depends on wall geometry, soil, slope, surcharge, seismic conditions, water, product system, and engineering. Use approved plans and qualified guidance.
Can I use the result to order immediately?
Treat it as a transparent planning takeoff. Reconcile corners, specialty units, exact product dimensions, plans, supplier increments, delivery, and site conditions before ordering.