Retaining Wall Block Calculator
How many retaining wall blocks, caps and base gravel a segmental block wall takes — counted course by course, the way the wall is actually built.
Result
| Courses | |
| Blocks per course | |
| Wall blocks (exact) | |
| Cap blocks | |
| Base gravel |
Units & conversions used
Imperial inputs are feet for the wall and inches for the block face; counts are whole blocks rounded up, and base gravel is shown in cubic yards (1 yd³ = 27 ft³). Metric inputs are converted first: 1 m = 3.28084 ft, 1 cm = 0.3937 in. The block count assumes dry-stacked blocks with no mortar gap, as segmental retaining wall systems are built.
Formula & source
Blocks per course = wall length(in) ÷ block length(in), rounded up
Blocks = courses × blocks per course × (1 + waste%)
Caps = blocks per course
Base gravel = length(ft) × 1 ft wide × 0.5 ft deep ÷ 27
Source: the course-by-course count is how segmental retaining wall (SRW) manufacturers' estimating guides lay out a wall. The base gravel figure assumes a compacted leveling trench 12 in wide and 6 in deep along the wall — the standard base detail in SRW installation guides. Block systems vary; always confirm counts against your block manufacturer's own chart before ordering.
Worked example (you can verify by hand)
Input: 20 ft long × 2 ft high wall, 16 × 6 in blocks, 0% waste.
- Courses: 24 in ÷ 6 in = 4
- Blocks per course: 240 in ÷ 16 in = 15
- Wall blocks: 4 × 15 = 60
- Cap blocks: one per block in the top course = 15
- Base gravel: 20 ft × 1 ft × 0.5 ft = 10 ft³ ÷ 27 = 0.37 yd³
Expected output: 60 blocks, 15 caps, 0.37 yd³ of base gravel.
Limitations — what this cannot do
- Enter the total wall height including the buried starter course — SRW walls are normally started with the first course partly or fully below grade for stability. If you enter only the exposed height, you will be one course short.
- This counts blocks, caps and base gravel only. It does not design the wall: geogrid reinforcement, drainage aggregate behind the wall, filter fabric and step-ups on sloped ground follow the block manufacturer's engineering and local code.
- Tall or load-bearing walls are engineered structures. Many jurisdictions require a permit and a design for walls over about 3–4 ft of exposed height, and surcharges (driveways, slopes above the wall) change the design entirely.
FAQ
How much do retaining wall blocks cost?
Standard segmental wall blocks commonly run in the $2–$6 range each at US home centers (2025–2026), with cap blocks priced similarly and larger or tumbled-look blocks higher. Gravel, drainage pipe and filter fabric are extra; for a small wall the base and drainage materials often add a noticeable share on top of the block bill — estimate them with our gravel calculator.
How high can I build a block retaining wall without engineering?
As a general guideline, simple gravity (dry-stacked, no geogrid) garden walls are commonly kept to about 3 ft of exposed height, and many local codes require a permit or engineered design above roughly 3–4 ft. This is not a design rule — soil, drainage and loads above the wall matter. Check your local code and the block manufacturer's height tables before building.
Do I really need a gravel base under the first course?
Yes. The compacted gravel pad (calculated above as a 12 in × 6 in trench) is what keeps the first course level and lets water drain instead of heaving the wall. Walls set directly on soil almost always go out of level within a few freeze–thaw seasons.
How much of the first course should be buried?
A common SRW guideline is to bury about 1 inch of wall height for every 8 inches of exposed wall, with at least one full course step below grade on level sites. Add that buried depth to the height you enter here so the course count includes it.