Retaining wall calculator
For a straight segmental block wall up to about 4 ft. Enter block dimensions from the manufacturer's spec sheet; base and drainage widths follow common installation guides.
Materials takeoff
Retaining Wall Calculator · https://estimahome.com/retaining-wall-calculator/
Wall length: 30 ftWall height, incl. buried course: 2 ft
- Courses
- 4
- Blocks per course
- 23
- Base gravel
- 1.28 cu yd
- Drainage stone
- 2.22 cu yd
| No. | Item | Qty | Unit | Unit cost | Amount |
|---|---|---|---|---|---|
| 1 | Wall block, 16 × 6 × 12 in | 97 | ea | $6.00 | $582.00 |
| 2 | Cap block | 23 | ea | $5.00 | $115.00 |
| 3 | Crushed stone, base and drainage | 3.5 | cu yd | $55.00 | $192.50 |
- Subtotal
- $889.50
- Likely range
- $756.08 – $1,022.93
- Bury the first course (often about 1 in per 8 in of wall height, at least one course). Include it in the height.
- Not included: drain pipe, filter fabric, construction adhesive for caps.
Buy these materials
Crushed stone is listed in the takeoff; order it in bulk from a landscape yard.
- 97 retaining wall blocksAmazon search for retaining wall blocks (opens in new tab)
- 23 wall cap blocksAmazon search for wall cap blocks (opens in new tab)
Links open a store search for each item. Check sizes and grades against your plan.
Quick reference
- A 30 ft wall of 16 in blocks takes 23 blocks per course.
- 2 ft of 6 in blocks is 4 courses, including the buried one.
- Block count = blocks per course × courses; caps = wall length ÷ cap length.
How it's calculated
⌈x⌉ means round up to the next whole unit; ⌊x⌋ means round down. Every quantity you buy is rounded up.
Blocks per course = ⌈ length × 12 ÷ block length ⌉Courses = ⌈ height × 12 ÷ block height ⌉Blocks = ⌈ blocks per course × courses × (1 + waste ÷ 100) ⌉Caps = ⌈ length × 12 ÷ cap length ⌉Base gravel (cu yd) = length × (block depth + trench extra) ÷ 12 × base depth ÷ 12 × (1 + compaction ÷ 100) ÷ 27Drainage stone (cu yd) = length × drain width ÷ 12 × height ÷ 27Gravel order = base + drainage, rounded up to ½ ydCost = Σ (quantity × unit price); range = cost × (1 ± range % ÷ 100)
Worked example
A 30 ft wall 2 ft tall with 16 × 6 in blocks has 4 courses of 23 blocks. With 5% waste that is 97 blocks plus 23 caps. The trench is 24 in wide with 6 in of base: 1.28 cu yd including 15% for compaction. 12 in of drainage stone behind the full height adds 2.22 cu yd, so order 3.5 cu yd of crushed stone. Materials at the default prices: $889.50.
Questions
How tall can I build a block retaining wall myself?
Most block makers and many codes allow about 3 to 4 ft without an engineered design. Taller walls, walls holding back a slope, driveway or structure, and tiered walls need engineering and often a permit.
Do I need gravel behind a retaining wall?
Yes. About 12 in of clean crushed stone behind the blocks lets water drain instead of building pressure behind the wall. Most installs also run a perforated drain pipe at the base.
How much of the wall goes below ground?
At least one course, or about 1 in for every 8 in of wall height. Include the buried course in the height you enter.
Cite: “Retaining Wall Calculator.” EstimaHome, https://estimahome.com/retaining-wall-calculator/. Updated 2026-10-20. Formulas in machine-readable form: /api/calculators.json.