BBuildculate
masonry

Retaining Wall Calculator

Estimate blocks, bricks, or stones, gravel leveling base volume, drainage gravel backfill, and material cost for building retaining wall structures.

CalculatorHow to CalculateFormulas & ExamplesFAQs

Select wall type, enter wall dimensions and excavation details, then calculate.

Interlocking concrete block retaining walls are durable, quick to install, and ideal for structural soil retention without mortar.

Wall Dimensions

Block Size

in
in
in

Foundation & Drainage Backfill

10%

Logistics & Cost Estimates (Optional)

lbs

Calculation Results

Awaiting Calculations

Fill in the retaining wall material type, dimensions, excavation inputs, and click Calculate to view estimates.

Formula Details

Wall Face Area Formula
Area = Length × Height

Calculates the total vertical surface face area of the retaining structure.

Variables Explained
  • Length
    Wall Length:Total horizontal span of the retaining wall.
  • Height
    Wall Height:Vertical height of the wall above the foundation.
Wall Volume Formula
Volume = Face Area × Wall Thickness

Determines the total three-dimensional structural volume of the wall.

Variables Explained
  • Face Area
    Surface Face Area:The calculated height multiplied by length.
  • Wall Thickness
    Thickness:Total depth of the masonry blocks or structural width of the wall.
Block/Brick/Stone Quantity Formula
Units Required = (Wall Volume / Nominal Unit Volume) × (1 + Waste / 100)

Divides total wall volume by the individual nominal volume of one unit. For brick retaining walls, a standard 3/8" (10mm) mortar joint is added to length and height to compute nominal volume. Concrete blocks and stones are calculated dry-stacked.

Variables Explained
  • Nominal Volume
    Nominal Unit Volume:Nominal Length × Nominal Height × Block Width.
  • Waste
    Waste Allowance:Added percentage for cuts, corner fittings, and shipping damage (typically 10%).
Gravel Base Volume Formula
Gravel Base Volume = Length × Wall Thickness × Gravel Base Thickness × (1 + Waste / 100)

Computes the volume of gravel needed for the foundational leveling trench beneath the wall blocks.

Variables Explained
  • Base Thickness
    Gravel Base Thickness:Thickness of the compacted leveling gravel layer (usually 6 inches).
  • Wall Thickness
    Trench Width:Assumed trench width matching the wall block thickness.
Backfill Volume Formula
Backfill Volume = Length × Height × Backfill Depth × (1 + Waste / 100)

Calculates the drainage aggregate backfill required behind the retaining structure for relieving hydrostatic pressure.

Variables Explained
  • Backfill Depth
    Backfill Depth:Thickness of the drainage zone behind the wall blocks (typically 12 inches).
Material Cost Formula
Estimated Cost = Units Required × Cost Per Unit

Estimates total cost based on the number of masonry blocks/bricks required.

Variables Explained
  • Cost Per Unit
    Unit Cost:The price of a single block, brick, or stone.

Calculation Example

Worked Example
Scenario

Calculate modular concrete blocks (16" L × 6" H × 12" W) and gravel base for a garden retaining wall measuring 30 feet long, 3 feet high, and 12 inches thick. Gravel base thickness is 6 inches. Backfill depth behind the wall is 12 inches. Assume 10% waste.

Calculation Steps
  1. 1.Calculate the total face area of the wall.
    Area = 30 ft × 3 ft = 90 sq ft
  2. 2.Convert wall thickness to feet and compute wall volume.
    Thickness = 12 in = 1.0 ft | Wall Volume = 90 sq ft × 1.0 ft = 90 cu ft
  3. 3.Compute nominal block volume in cubic feet.
    Nominal Length = 16 in = 1.333 ft | Nominal Height = 6 in = 0.5 ft | Width = 12 in = 1.0 ft | Nominal Volume = 1.333 × 0.5 × 1.0 = 0.667 cu ft
  4. 4.Calculate raw blocks, apply 10% waste, and round up.
    Raw Count = 90 / 0.667 = 135 Blocks | Blocks Required = 135 × 1.10 = 148.5 => 149 Blocks
  5. 5.Calculate compacted gravel base trench volume and convert to cubic yards.
    Base Volume = 30 ft × 1.0 ft × 0.5 ft (6 in) × 1.10 = 16.5 cu ft | In cubic yards = 16.5 / 27 = 0.61 cu yd
  6. 6.Calculate drainage backfill volume behind the wall and convert to cubic yards.
    Backfill Volume = 30 ft × 3 ft × 1.0 ft (12 in) × 1.10 = 99 cu ft | In cubic yards = 99 / 27 = 3.67 cu yd
Final Quantity Needed149 Blocks, 16.5 cu ft (0.61 cu yd) of Gravel Base, and 99 cu ft (3.67 cu yd) of Backfill
Worked Example
Scenario

Calculate standard bricks (7.625" × 2.25" × 3.625") for a brick retaining wall measuring 15 feet long, 2 feet high, and 8 inches thick, assuming a 3/8" (0.375") mortar joint, 6" gravel base, 12" backfill depth, and 10% waste.

Calculation Steps
  1. 1.Calculate the total face area of the wall.
    Area = 15 ft × 2 ft = 30 sq ft
  2. 2.Convert wall thickness to feet and compute wall volume.
    Thickness = 8 in = 0.667 ft | Wall Volume = 30 sq ft × 0.667 ft = 20 cu ft
  3. 3.Determine nominal brick dimensions by adding the 3/8" joint and compute volume in cubic feet.
    Nominal Length = 7.625" + 0.375" = 8.0" (0.667 ft) | Nominal Height = 2.25" + 0.375" = 2.625" (0.21875 ft) | Width = 3.625" (0.302 ft) | Nominal Volume = 0.667 × 0.21875 × 0.302 = 0.0441 cu ft
  4. 4.Calculate raw brick count, apply 10% waste, and round up.
    Raw Count = 20 / 0.0441 = 454 Bricks | Bricks Required = 454 × 1.10 = 499.4 => 500 Bricks
  5. 5.Compute gravel leveling base trench volume.
    Base Volume = 15 ft × 0.667 ft × 0.5 ft (6 in) × 1.10 = 5.5 cu ft (0.20 cu yd)
  6. 6.Compute drainage backfill volume behind the brick structure.
    Backfill Volume = 15 ft × 2 ft × 1.0 ft (12 in) × 1.10 = 33 cu ft (1.22 cu yd)
Final Quantity Needed500 Bricks, 5.5 cu ft (0.20 cu yd) of Gravel Base, and 33 cu ft (1.22 cu yd) of Backfill
Worked Example
Scenario

Calculate metric quantities for a stone block retaining wall measuring 12 meters long, 1.5 meters high, and 30 cm thick. Use standard stone block units (300 × 100 × 200 mm), a gravel base thickness of 15 cm, backfill depth of 30 cm, and 10% waste factor.

Calculation Steps
  1. 1.Calculate wall face area.
    Area = 12 m × 1.5 m = 18 sq m
  2. 2.Calculate wall volume.
    Thickness = 30 cm = 0.3 m | Wall Volume = 18 sq m × 0.3 m = 5.4 cu m
  3. 3.Compute individual stone volume in cubic meters.
    Length = 300 mm = 0.3 m | Height = 100 mm = 0.1 m | Width = 200 mm = 0.2 m | Stone Volume = 0.3 × 0.1 × 0.2 = 0.006 cu m
  4. 4.Compute raw stone count, apply 10% waste, and round up.
    Raw Count = 5.4 / 0.006 = 900 Stones | Stones Required = 900 × 1.10 = 990 Stones
  5. 5.Compute leveling trench gravel volume.
    Base Volume = 12 m × 0.3 m × 0.15 m (15 cm) × 1.10 = 0.594 cu m
  6. 6.Compute drainage gravel backfill volume.
    Backfill Volume = 12 m × 1.5 m × 0.3 m (30 cm) × 1.10 = 5.94 cu m
Final Quantity Needed990 Stones, 0.594 cu m of Gravel Base, and 5.94 cu m of Backfill

How to Use

Follow these steps to estimate blocks, gravel leveling pad, backfill volume, and overall costs for your retaining wall construction:

  1. Select Material Type: Choose Concrete Block, Brick, or Stone to load presets and explanations.
  2. Choose Unit System: Toggle between Imperial (ft/in/yd) and Metric (m/cm/mm) at the top right of the calculator.
  3. Enter Wall Dimensions: Input the total length and height of the wall, along with the wall thickness.
  4. Select or Enter Unit Sizes: Select a standard preset or choose "Custom Size" to enter your specific block/brick length, height, and width.
  5. Enter Foundation & Backfill: Enter the gravel base trench thickness (e.g. 6 inches) and the drainage backfill depth behind the wall (e.g. 12 inches).
  6. Enter Waste and Logistics: Slide the waste allowance (10% is recommended) and optionally input unit weight and cost per block.
  7. Calculate: Click Calculate to view all results on the right side. Click Reset to clear the form.

Frequently Asked Questions

How many retaining wall blocks do I need?
To estimate the number of blocks, divide the total volume of your retaining wall by the volume of a single block. For brick walls, standard practice is to add the mortar joint thickness (commonly 3/8" or 10mm) to the length and height dimensions to calculate the nominal unit volume, whereas concrete blocks and stone are typically calculated dry-stacked.
How much backfill is required?
Retaining walls require a layer of clean gravel backfilled immediately behind the blocks to allow water to drain away. This backfill volume is calculated as the length of the wall multiplied by the wall height and the desired backfill depth (typically 12 inches or 30 cm). Adding a waste factor of 10% is recommended for compaction and settling.
How thick should the gravel base be?
A solid gravel base is essential to prevent the retaining wall from settling or tilting over time. Generally, a trench is dug along the length of the wall, and a compacted gravel leveling pad of 4 to 6 inches (10 to 15 cm) is laid down. The width of the trench usually matches the thickness of the retaining wall block.
Why should I include a waste percentage?
You should add a waste percentage (usually 10%) to account for damaged blocks, chips during shipping, and cuts that must be made at the ends of rows or around curves. Waste allowance ensures you do not run out of materials mid-construction.
Can I use custom block sizes?
Yes. In the Preset dropdown, choose 'Custom Size...' to manually enter your block, brick, or stone dimensions. The fields for Length, Height, and Width will become editable so you can calculate requirements for any size of masonry block.
How accurate is the material estimate?
This calculator provides a precise geometric estimation. Real-world needs might vary slightly based on block design (e.g., overlapping lip, hollow core blocks, batter angle setback which slants the wall slightly backward) and grading. Always consult with a licensed contractor for tall or critical structural walls.

Explore more construction calculators

Estimate aggregate concrete slabs, soil excavation volumes, rebar grids, masonry bricks, and building material costs to successfully plan your structures.

View CategoriesAbout Buildculate

Recommended Calculators

Similar Tools
masonryActive

Brick Calculator

Calculate brick count, mortar requirements, and project costs for brick walls.

Open Calculator
masonryActive

Concrete Block Calculator

Estimate the number of concrete blocks, required mortar volume, and material cost for building CMU walls.

Open Calculator
masonryActive

Wall Material Calculator

Calculate bricks, blocks, cement, sand, and mortar for building complete masonry walls.

Open Calculator
materialActive

Aggregate & Gravel Calculator

Calculate aggregate, gravel, and crushed stone quantities for driveways, foundations, drainage, and landscaping.

Open Calculator
materialActive

Concrete Calculator

Calculate concrete volume, weight, and bag quantities for common construction shapes.

Open Calculator
Disclaimer

Calculations are estimates based on the values you enter and standard engineering formulas. Results are intended for planning and estimation only. Always verify critical measurements, specifications, and local building requirements before purchasing materials or beginning construction.