🏯Retaining Wall Calculator
Count wall blocks, caps, gravel backfill and drain pipe for a block retaining wall.
Your wall
You'll need about
220 blocks
10 courses (incl. 1 buried) × 20 blocks · 10% waste
⚠️ Walls over 3–4 ft (about 1–1.2 m) may require an engineer or a permit, depending on local rules. Check with your city before you build.
caps
22
gravel cubic yards
3.21
pipe ft
22
courses
10
🛒 Shopping list
- Wall blocks (12 × 4 in face)220 blocks
- Cap blocks22 caps
- Gravel for base & backfill3.21 cu yd
- Perforated drain pipe (4 in)22 ft
Bury the first course and fill behind the wall with gravel so water drains away instead of pushing on your blocks.
How it works
Courses = wall height ÷ block height + 1 buried course. Blocks = courses × (wall length ÷ block length), plus waste. Caps = wall length ÷ cap length. Gravel covers a 1 ft zone behind the wall plus a 2 ft × 6 in base trench. Drain pipe runs the length of the wall plus 10%.
Walls over 3–4 ft may require an engineer or a permit, depending on local rules.
Worked example
A 20 ft wall, 3 ft tall, 12 × 4 in blocks with caps:
- 36 ÷ 4 = 9 courses + 1 buried = 10 courses × 20 blocks = 200, plus 10% = 220 blocks
- 22 caps
- 3.21 cu yd of gravel and 22 ft of drain pipe
Questions people ask
Many areas allow walls up to 3–4 ft without an engineer. Taller walls usually need a design and a permit.
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Last updated September 28, 2026. These results are friendly estimates to help you plan — always double-check before buying or making big decisions.