Masonry / Segmental retaining walls
Retaining Wall Block Calculator
Estimate segmental retaining-wall blocks, cap units, compacted base aggregate, drainage aggregate, pallets, and optional material cost from dimensions you already know.
Estimate retaining-wall blocks and materials
Enter straight wall runs and exact product dimensions. Add only the base, drainage, caps, supplier data, and rates specified for your project.
Wall sections
Enter exposed block-face height without the cap. Add buried courses only when they are shown by the approved plan or selected wall system.
Selected wall units
Use the installed horizontal face coverage from the exact product.
Use the installed course rise from the exact product.
Applied after whole courses and end units are calculated.
Base and drainage — optional
The calculator does not choose these dimensions. Enable a material only when its width or depth is known from the approved detail.
Supplier and cost inputs — optional
Leave blank when blocks are ordered individually or supplier packaging is unknown.
Optional material-only price.
Wall block order
- Base wall blocks
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- Allowance blocks
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- Wall blocks to order
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- Cap units to order
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- Whole pallets
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Wall takeoff basis
- Total straight wall run
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- Exposed wall face
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- Calculated face including buried courses
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- Drain-pipe planning length
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Optional material cost
- Wall blocks
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- Cap units
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- Base aggregate
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- Drainage aggregate
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- Material subtotal
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View section schedule and copyable summary
Enter the exact block face dimensions to see the material schedule.
Method
How the retaining wall block calculator works
This tool is for straight runs built with segmental retaining-wall units. It counts each run course by course, adds only the buried courses you enter, and keeps block allowance separate from the base quantity.
- Exposed courses = exposed block-face height ÷ installed block height, rounded up
- Total courses = exposed courses + user-entered buried courses
- Blocks per course = wall length ÷ installed block face length, rounded up
- Base wall blocks = blocks per course × total courses × identical sections
- Order blocks = base wall blocks + user allowance, rounded up once
Separate wall runs round independently. A partial unit left at the end of one terrace or isolated section is not automatically treated as a usable unit in another run.
Blocks, caps, base, and drainage are separate quantities
Wall blocks and cap units are whole products. The base and drainage zones are volume quantities. The calculator therefore reports each material independently rather than combining everything into one generic “retaining wall material” number.
Base aggregate uses the wall-run length, entered base width, and entered compacted depth. Drainage aggregate uses the entered width behind the wall and the calculated full block height, including the buried courses you supplied. Each aggregate can have its own allowance because compaction, handling, and ordering conditions differ from block breakage.
Worked example
Retaining wall material calculation example
Consider a straight 10 m wall with 1.2 m of exposed block face, one buried course, and blocks that cover 400 mm horizontally by 200 mm vertically. The exposed height requires six courses. Adding the buried course gives seven courses, and the wall needs 25 blocks per course.
The base quantity is therefore 175 blocks. A user-selected 5% allowance produces 183.75 blocks, rounded once to 184 blocks to order. A 500 mm cap covers the run with 20 base caps and 21 caps after the same allowance.
If the approved detail specifies a 600 mm wide by 150 mm deep base, its net geometric volume is 0.90 m³. A 300 mm drainage zone over the calculated 1.40 m total block height is 4.20 m³. Those values remain separate from any allowances you choose.
Use the exact retaining-wall system and approved details
Segmental retaining-wall products vary in face length, course height, cap dimensions, setback, unit depth, core configuration, and minimum-radius limitations. Copy installed coverage from the current product documentation instead of treating a catalogue name as a universal size.
The Allan Block material-estimation worksheet demonstrates course and unit estimation for its named systems and directs users to approved plans for buried block, aggregate, reinforcement, and pipe quantities. Those details are product- and project-specific, so this calculator exposes them as inputs rather than defaults.
The CMHA segmental retaining-wall guidance explains that drainage features, gravel fill, wall batter, unit behavior, and stability depend on site and system design. The CMHA sample specifications likewise tie leveling-pad and gravel-fill dimensions to the construction drawings. These sources do not certify this calculator.
Material cost is not an installed retaining wall quote
Optional prices apply only to the calculated order quantities you enable: blocks, caps, base aggregate, and drainage aggregate. The subtotal excludes labor, excavation, disposal, delivery, equipment, geotextile, reinforcement, engineering, permits, tax, and other project costs unless you account for them elsewhere.
Currency is only a label for your entered rates. ConstructGauge does not supply live or regional retaining-wall prices.
Assumptions and limitations
- Every entered section is a straight run using the same selected wall block and cap system.
- Exposed height describes the block face below any separate cap unit.
- Courses and end units round up independently for each separate wall section.
- Buried courses come from the user’s approved plan or manufacturer-system detail; the calculator does not select them.
- Base and drainage quantities are rectangular geometric volumes from user-entered dimensions.
- The drainage calculation does not subtract block cores, pipe displacement, steps, batter, corners, fabric, or other details.
- The optional pipe result is only the summed straight wall-run length, not a drainage layout or purchase recommendation.
- The calculator does not determine soil properties, bearing, sliding, overturning, global stability, surcharge, geogrid, reinforcement, drainage capacity, wall batter, allowable height, or code compliance.
Retaining wall block calculator FAQ
How many retaining wall blocks do I need?
Divide the exposed height by the installed block height to find whole exposed courses, add the buried courses required by the project, and divide each wall length by the installed block face length. Round courses and end units up for each separate run before adding an allowance.
Does the calculator decide how many courses must be buried?
No. Enter buried courses only from the approved plan or the selected manufacturer’s applicable system detail. Embedment depends on the wall, grade, product, soil, climate, and design conditions.
How are cap blocks calculated?
Each straight section length is divided by the installed cap length and rounded up. The selected block-and-cap allowance is then applied to the combined base cap quantity.
How does it calculate base aggregate?
Base aggregate is wall-run length multiplied by the base width and compacted depth you enter. It is a geometric quantity and does not select the correct base material or dimensions.
How does it calculate drainage aggregate?
Drainage aggregate is wall-run length multiplied by the width you enter and the calculated block height, including entered buried courses. Confirm the actual zone, block-core fill, pipe, fabric, and drainage detail separately.
Can I use this for a curved retaining wall?
Not as a radius calculator. You may enter a measured developed run length, but tapered units, course setback, cuts, minimum radius, and changing course lengths require the exact product layout. A dedicated circular mode is not included.
Is this the same as the concrete block calculator?
No. The Concrete Block Calculator estimates conventional CMUs and laying mortar for ordinary walls. This page estimates segmental retaining-wall courses, caps, base aggregate, and drainage aggregate. For grout inside hollow CMU cores, use the Concrete Block Fill Calculator.
BOQ use and calculation basis
The primary BOQ-ready result is the whole orderBlocks quantity for “Segmental retaining-wall blocks,” with the calculated base blocks and allowance retained separately. Caps are another whole-unit line item. Base and drainage aggregate remain independent cubic-metre quantities, and the optional wall-run pipe basis remains a metre quantity.
The pure calculation engine returns finite, unformatted values in canonical SI units. A future BOQ adapter can select the applicable lines without parsing the interface, combining different aggregates, or treating supplier pallets and material prices as physical net quantities.