Free estimate — verify against local code before building
Retaining Wall Calculator
Estimate whole blocks, caps, base and drainage gravel, fabric, pipe, adhesive, weight, and cost. This is a materials takeoff—not a structural wall design.
What this calculator includes
Enter the wall geometry and exact block system dimensions to estimate full courses, whole blocks and caps, leveling-pad and drainage gravel, optional filter fabric, drain pipe, adhesive, total material weight, and editable material cost. The calculator is a quantity takeoff only: it does not check sliding, overturning, bearing, global stability, drainage capacity, soil reinforcement, or geogrid design.
How to use this retaining wall calculator
- 01
Enter wall and embedment
Measure wall length and exposed retained height. Enter buried full courses or a planned embedment depth from an approved manufacturer detail or engineered plan.
- 02
Copy the exact product data
Enter block face width, height, depth, weight, and price plus cap dimensions, weight, and price. Nominal product families vary enough that labels and approved details must control.
- 03
Define base and drainage zones
Use the leveling-pad and drainage-zone dimensions on the approved detail. Enter supplier densities and prices to convert cubic yards into purchased tons and cost.
- 04
Review the whole order
Check exact geometry, full-course rounding, waste, blocks, caps, bulk aggregate, bag alternatives, fabric, pipe, adhesive, delivered weight, and access before buying.
Calculation sources and review
Primary references and formula assumptions are linked so you can verify them against the selected product, supplier, and adopted local requirements.
Internal formula review completed July 13, 2026. What this review covers
- CMHA Segmental Retaining Wall Installation Guide (opens in a new tab)
General installation sequence, leveling pad, drainage fill, drain pipe, and site-specific engineering guidance.
- 2021 IRC Section R404.4 — Retaining Walls (opens in a new tab)
Professional-design triggers for walls retaining more than 48 inches or resisting added lateral loads.
- OSHA Trenching and Excavation (opens in a new tab)
Excavation cave-in hazards and protective-system requirements.
Frequently asked questions
How many retaining wall blocks do I need?
Divide wall length by block face width to get blocks per course, round up to a whole block, multiply by the full course count including embedment, then add cutting and breakage waste. This calculator exposes each step.
How much of the first course should be buried?
Embedment is product- and site-specific. Many systems require at least one full buried course, with more embedment for taller walls or slopes. Use the approved manufacturer detail or engineered plan rather than a universal rule of thumb.
How much drainage gravel goes behind a retaining wall?
The required zone depends on the wall design and groundwater conditions. CMHA guidance commonly illustrates clean gravel fill extending at least 12 inches behind segmental units, but the wall designer and manufacturer detail govern.
When does a retaining wall need an engineer or permit?
Rules vary locally. The 2021 IRC calls for accepted engineering practice when an unsupported wall retains more than 48 inches of unbalanced fill, or when a wall over 24 inches resists added lateral loads. Surcharges, slopes, poor soils, water, property lines, and tiered walls can trigger review at lower heights.
Does drainage gravel replace a drainage design?
No. Gravel and a perforated pipe address incidental water only when correctly filtered and discharged. Surface drainage, groundwater, outlets, erosion, and hydrostatic pressure require site-specific review.