How to calculate your retaining wall project
Segmental retaining walls are planned by course and by the installed face size of the selected block. This calculator adds full courses, an adjustable buried base course, caps, and base gravel for a first-pass material takeoff.
- Measure the wall length along its face and the visible height from finished grade.
- Enter the installed face width and height of the exact wall block, plus the cap length.
- Confirm buried courses and gravel-base dimensions against the manufacturer design and local requirements.
Formula
The calculation
Wall length is divided by block face width and visible height is divided by block face height; both values round up to full blocks and courses. Buried courses and waste are then added. Cap blocks and base gravel are calculated separately.
Worked example
A 20 ft wall that is 3 ft high using 12 × 6 inch block faces has 6 visible courses and 20 blocks per course. With one buried course and 10% extra, plan for 154 wall blocks.
The result is a planning estimate. Round purchasing quantities up to available package sizes and confirm the exact product specifications.
Material assumptions
- The starting design includes one buried course, 12 × 6 inch block faces, and a 24 × 6 inch gravel base.
- Block cost excludes caps, aggregate, drainage stone, pipe, geogrid, adhesive, delivery, and labor.
- This quantity tool is not an engineering or code-compliance design.
Read the complete calculator methodology for unit conversions, rounding rules, and limitations.
Why the waste factor matters
A waste or extra-material percentage allows for real-world variation: irregular edges, cuts, compaction, settling, spillage, and measurement error. Ten percent is a useful starting point, not a universal rule. Increase or reduce it according to the material, layout, and supplier guidance.
Unit conversions used
Questions
Retaining Wall Calculator FAQ
How many retaining wall blocks do I need?
Multiply full blocks per course by the number of visible and buried courses, then add waste. The calculator rounds dimensions up so partial rows do not undercount materials.
Does a retaining wall need a buried course?
Many segmental systems begin with part or all of the first course below grade, but the exact embedment depends on wall height, slope, soil, and manufacturer instructions.
When does a retaining wall need engineering?
Height limits, surcharges, slopes, soil, drainage, and local codes can trigger engineered design or permits. Confirm requirements before construction.