Retaining Wall Blocks
Free Retaining Wall Blocks calculator with clear step-by-step results.
About Retaining Wall Blocks
Block count comes from courses times blocks per course, and the courses figure has to include the base courses buried below grade - typically one for every 200 mm of exposed height. Drainage gravel is sized as a 300 mm zone behind the full wall height, since inadequate drainage is the usual cause of retaining wall failure.
Formulas
Courses required
Courses = ceil(exposed height / block height) + buried courses
Blocks required
Blocks = ceil(courses x ceil(length / block length) x (1 + waste))
Worked example
With the default values below, Retaining Wall Blocks returns Wall blocks to buy of 137. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Wall lengthminimum 0.1 m
- 8 m
- Exposed wall heightminimum 0.1 m
- 1.2 m
- Block lengthminimum 100 mm
- 450 mm
- Block heightminimum 50 mm
- 200 mm
- Courses buried below gradeaccepts 0–5
- 1
- Waste and cutting allowanceaccepts 0–30 %
- 8 %
Results
- Wall blocks to buy
- 137 blocks
- Courses including buried base
- 7 courses
- Cap blocks
- 19 blocks
- Drainage gravel behind the wall
- 3.70 m3
Step by step
- 1Values used
- 2Courses required
- 3Blocks required
- 4Wall blocks to buy= 137 blocks
- 5Courses including buried base= 7 courses
- 6Cap blocks= 19 blocks
- 7Drainage gravel behind the wall= 3.70 m3
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- Retaining walls carry significant loads and their failure can be dangerous. Walls above the height permitted locally, or with any surcharge behind them, must be designed by a qualified engineer and permitted.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Retaining walls carry significant loads and their failure can be dangerous. Walls above the height permitted locally, or with any surcharge behind them, must be designed by a qualified engineer and permitted.
Frequently Asked Questions
How deep should the base course be?
A common rule is one buried course for every 200 mm of exposed wall, on a compacted granular base at least 150 mm thick. Sloping ground and poor soils need more.
When do I need engineering input?
Generally above about 1.2 m exposed height, or any height with a surcharge such as a driveway, slope or structure behind the wall. Most jurisdictions require a permit and design above that threshold.