Retaining Wall Calculator
Enter your wall length, height, and block size to estimate the number of blocks, the number of courses, and the base gravel needed for a segmental retaining wall.
Results
- Blocks needed
- 111
- Courses
- 5
- Blocks per course
- 20
- Base gravel (6 in)
- 0.37 cu yd
Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.
Enter your wall length, height, and block size to estimate the number of blocks, the number of courses, and the base gravel needed for a segmental retaining wall.
How to use the retaining wall calculator
- Enter the wall length in ft.
- Enter the wall height in ft.
- Enter the block length in in.
- Enter the block height in in.
- Enter the waste factor in %.
- Optionally add a price to estimate the total project cost.
- Read your quantities instantly — no sign-up, and you can print the estimate to take to the supplier.
Worked example
Inputs
- Wall length
- 20 ft
- Wall height
- 3 ft
- Block length
- 12 in
- Block height
- 8 in
- Waste factor
- 10 %
Results
- Blocks needed
- 111
- Courses
- 5
- Blocks per course
- 20
- Base gravel (6 in)
- 0.37 cu yd
Using the example values above, the retaining wall calculator returns 111 (blocks needed). Change any field to match your own project and the numbers update instantly.
How much extra should I order?
Always order a little extra. A 5% waste factor suits simple, square projects; 10% is right for most jobs; bump it to 15–20% for irregular shapes, diagonal patterns, or uneven ground. Running short almost always costs more than the leftover material.
Formula
Blocks per course = wall length ÷ block length. Courses = wall height ÷ block height. Blocks = courses × blocks per course, × (1 + waste%).
Frequently asked questions
- How many retaining wall blocks do I need?
- Divide the wall length by the block length for blocks per course, then multiply by the number of courses (wall height ÷ block height).
- How deep should the base of a retaining wall be?
- Set the first course on 4–6 inches of compacted gravel, with the bottom course buried about one tenth of the wall height.
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