Retaining Wall Block Calculator

Divide each wall section into courses, round the blocks in each course up, then add typically 5% waste for a simple straight layout and more for curves or cuts.

This calculator returns blocks, caps, base and drainage aggregate, core fill, fabric, adhesive, pipe, fittings, approved-plan geogrid, supplier order units, and an itemized cost.

Material estimator only. Retaining walls can fail from soil pressure, poor drainage, surcharge loads, slopes, frost, and weak foundations; follow approved plans, local code, and manufacturer instructions.

Project inputs

Essential measurements

Unit system

Currency

Block preset

Planning examples only. Confirm face coverage, setback, minimum radius, and pattern rules on the product data sheet.

General block waste (%)

5% is a straight-wall starting allowance; section cutting waste is added separately.

Wall section 1

Section name

Layout

Centerline length ft

Measure along the block-face centerline.

Height measurement

Measured height ft

Caps sit above this height in visible-height mode.

Buried courses

Whole block courses below finished grade.

Extra curve/cutting waste (%)

Optional: block product, caps, and layout details

Block quantity method

Block face length in

Block face height in

Block depth in

Used for optional block-core fill volume.

Cap row

Cap face length in

Cap installed height in

Cap waste (%)

Total return/wing-wall length ft

Adds the entered length at the weighted-average wall height.

Extra corner/step-up blocks

Enter the product-specific units needed for corners, steps, or exposed ends.

Optional: base, drainage, fabric, core fill, and approved geogrid

Base trench width in

Compacted base depth in

Drainage stone width in

Drainage height

Loose/compaction allowance (%)

Base density tons/yd³

Drainage stone density tons/yd³

Drain pipe

Pipe diameter in

Outlet allowance ft

Outlet fittings

Filter fabric

Fabric overlap/cut allowance (%)

Block core void (%)

Set above 0 only when the product requires aggregate-filled cores.

Approved-plan geogrid area sq ft

Order-only input; this tool never chooses geogrid length or strength.

Approved number of geogrid layers

Optional: supplier units and separate prices

Blocks per pallet

Block price unit

Wall block price

Caps per pallet

Cap price unit

Cap price

Aggregate order increment yd³

Minimum aggregate order tons

Aggregate per bag yd³

Base price unit

Base aggregate price

Drain stone price unit

Drainage stone price

Core-fill volume per bag yd³

Core-fill price per bag

Pipe stock length ft

Pipe price per stock length

Fitting price each

Fabric area per roll sq ft

Fabric price per roll

Adhesive coverage per tube ft

Adhesive price per tube

Geogrid area per roll sq ft

Geogrid price per roll

Delivery allowance

Optional: site conditions and safety flags

Driveway, structure, fence, or other surcharge Slope above or below wall Poor, expansive, or unknown soil High water, seepage, or poor drainage Tiered or terraced wall

Purchase-ready estimate

Calculating the example…

Visible block height--

Buried depth--

Block-stack height--

Cap height--

Overall finished height--

Wall blocks: calculated + waste → order--

Caps: calculated + waste → order--

Base: raw + allowance → order--

Drain stone: raw + allowance → order--

Filter fabric--

Drain pipe--

Block-core fill--

Approved-plan geogrid--

Cost status--

Front-elevation check

Combined bill of materials

Material	Calculated	Waste / allowance	Order quantity	Order unit	Unit price	Subtotal

Section summary

Calculation method and evidence

This is a quantity takeoff for dry-stacked segmental retaining wall units, not a stability design. The 24 in wide by 6 in deep base, 12 in drainage zone, filled-core option, and drain warning are editable planning assumptions supported by current VERSA-LOK installation guidance and Allan Block residential installation guidance. Those details are system- and site-dependent; the selected manufacturer's instructions and approved plan control.

visible courses = ceiling((measured height − cap height when included) / block face height)
total courses = visible courses + buried courses
blocks per course = ceiling(centerline length / block face length)
calculated blocks = total courses × blocks per course + entered detail blocks
waste blocks = ceiling(calculated blocks × combined waste %)
order blocks = ceiling((calculated + waste) / blocks per pallet) × blocks per pallet
compacted aggregate volume = length × width × height; allowance and supplier rounding are applied afterward
tonnage = rounded order volume × entered supplier density

Each section is rounded before its totals are combined, because partial courses and partial blocks cannot usually be shared across dissimilar sections. Waste is shown as a separate whole-unit quantity. Aggregate “raw” volume is the compacted rectangular takeoff; the loose/compaction allowance is added before rounding to the entered supplier increment. Density is only a volume-to-weight conversion, and moisture, gradation, excavation, stock sizes, breakage, minimum orders, and supplier packaging can change the purchase quantity.

Geogrid rule: this tool only rounds the approved-plan area entered by the user. It does not infer reinforcement from height. Allan Block states that grid location and embedment depend on site conditions, height, and grid strength and should follow approved plans or an engineer; see its reinforced-soil-wall guidance.

Show the calculation for my current inputs

Calculate to generate a checkable explanation.

How to use the estimate

1. Split the layout

Add a section whenever length, height, or curve type changes. Measure curves on the block-face centerline; enter radius only for a complete circle.

2. Define height

Choose whether the measured height stops at the top of the block face or includes the cap. Buried courses are always added below grade.

3. Match the product

Use face dimensions, manufacturer blocks-per-area data, or a complete multi-size pattern's coverage. Confirm every preset on the current data sheet.

4. Set purchase units

Enter pallet counts, stock lengths, roll coverage, order increments, minimum tonnage, and separate prices from the supplier quote.

Worked example: 40 ft × 3 ft visible wall

Convert the block: an 18 × 8 in face is 1.5 ft long × 0.667 ft high.
Blocks per course: ceiling(40 ÷ 1.5) = 27.
Courses: ceiling(3 ÷ 0.667) = 5 visible courses; add 1 buried course = 6.
Blocks before waste: 27 × 6 = 162.
Waste: ceiling(162 × 5%) = 9; calculated purchase quantity before pallet rounding = 171.
Supplier order: with 48 blocks per pallet, ceiling(171 ÷ 48) = 4 pallets, or 192 blocks.
Caps: ceiling(40 ÷ 1.5) = 27; 8% waste adds 3; a 48-cap pallet setting rounds the order to 48 caps.
Base: 40 × 2 × 0.5 = 40 ft³ = 1.48 yd³ compacted; add 10% = 1.63 yd³; round to a 0.25 yd³ increment = 1.75 yd³, or 2.63 tons at 1.5 tons/yd³.
Drainage stone: 40 × 1 × 4 = 160 ft³ = 5.93 yd³ compacted; add 10% and round to 0.25 yd³ = 6.75 yd³, or 10.13 tons.
Other materials: the defaults produce 184 sq ft of fabric before roll rounding, 46 ft of pipe rounded to five 10 ft lengths, and two adhesive tubes at 30 ft of coverage per tube.
Cost: multiply each rounded order quantity by its matching entered unit price. Until all included prices are entered, the result is labeled a subtotal and lists what is missing.

Quick reference for common wall and block sizes

One buried course, straight wall, 5% waste, no corner extras. Product geometry and supplier packs vary.

Visible wall size	Block face	Visible + buried courses	Blocks/course	Before waste	With 5% waste
10 ft × 2 ft	18 × 8 in	3 + 1	7	28	30
20 ft × 3 ft	18 × 8 in	5 + 1	14	84	89
40 ft × 4 ft	18 × 8 in	6 + 1	27	189	199
20 ft × 3 ft	16 × 6 in	6 + 1	15	105	111
10 ft × 2 ft	12 × 4 in	6 + 1	10	70	74

Validation against manual arithmetic

Test	Manual result before pallet rounding	Calculator result
40 ft × 3 ft straight example	162 + 9 waste = 171	171
8 ft radius circle × 2 ft visible	34/course × 4 courses = 136; +7 = 143	143
10 ft × 2 ft plus 20 ft × 3 ft	28 + 2 waste + 84 + 5 waste = 119	119

Retaining Wall Block FAQ

Is the first retaining wall course included?

Yes. The buried allowance is converted to whole courses and included in the block stack. The result separates visible height, buried depth, and total block-stack height so the first course is not silently omitted.

How should I measure a curved retaining wall?

Measure along the block-face centerline and choose inside curve or outside curve. For a complete circle, choose circular wall and enter the centerline radius; the calculator uses 2 × pi × radius. Add cutting waste for tight curves, returns, corners, and step-ups.

Do cap blocks add to retaining wall height?

Usually, yes. In visible-height mode the cap sits above the entered height. In finished-height mode the calculator subtracts the entered cap height to find the visible block-face height, then displays both values separately.

How much block waste should I use for straight and curved walls?

A simple straight wall often starts near 5 percent planning waste. Curves, corners, returns, steps, patterns, and color blending can require more; enter extra cutting waste for each section and confirm the order with the supplier.

How do I calculate a multi-size retaining wall pattern?

Choose multi-size pattern coverage and enter the manufacturer-stated square feet or square metres covered by one complete pattern set, plus the number of units in that set. Use the product data sheet because mixed patterns cannot be inferred reliably from one block's dimensions.

What does gravel density mean?

Density converts aggregate volume to weight. Gradation, moisture, source, and compaction change it, so use the supplier's tons per cubic yard or tonnes per cubic metre. The calculator keeps raw compacted volume, allowance, order volume, and tonnage separate.

Are filter fabric and drain pipe included?

Yes, when enabled. Fabric uses wall length times drainage height plus overlap, and pipe uses wall length plus outlet allowance rounded to the chosen stock length. Diameter and outlet-fitting quantity remain user inputs from the approved detail.

Does the calculator design geogrid?

No. It only orders the approved-plan area and number of layers that you enter. Geogrid strength, length, spacing, and connection depend on the wall system, soil, loading, slopes, water, and engineered design.

Can I use this calculator for a mortared CMU wall?

No. This tool is for dry-stacked segmental retaining wall units. Mortared concrete masonry walls require footing, reinforcement, grout, mortar, drainage, and structural calculations that this estimator does not perform.

Accountability, limits, and safety

Author: Starlight Tools, published by Starlight Robotics. Last updated: July 17, 2026.

Methodology: deterministic geometry and supplier-pack rounding, checked against the manual cases above and the linked manufacturer installation guidance. No professional reviewer is claimed.

Correction policy: calculation corrections are reproduced with saved inputs, compared with the written formulas and cited primary sources, and disclosed through the updated date and visible methodology. Product-specific defaults are changed only when supported by current manufacturer documentation.

This tool does not check soil pressure, sliding, overturning, bearing, global stability, frost, seismic loads, drainage capacity, or code compliance. Height thresholds are jurisdiction-specific and may count the buried wall or footing. As one illustration—not a universal rule—the 2025 California Building Code Section 105.2 exempts certain retaining walls not over 4 ft measured from the bottom of the footing to the top of the wall, but not when supporting a surcharge; local amendments can be stricter.

Privacy: inputs stay in your browser; the page does not upload calculator values.
Use approved details: surcharge, slopes, poor soil, high water, tiering, and taller walls can require permits, drainage design, reinforcement, and a qualified engineer even below a commonly cited height.
Purchase check: confirm product coverage, color-lot blending, corner units, minimum curve radius, delivery access, taxes, and return policy with the supplier.