You need
- 4 × 20rows × blocks
- 0.9tons of base
- 3.5tons of wall rock
Prices: what dealers and stone yards post, October 2026.
Stop here
This wall needs an engineer
- For a wall 30 ft long and 2 ft tall, get 80 blocks and 20 caps.
- That is 4 rows of 20. The bottom row goes in the ground.
- Under the wall: 0.9 tons of crusher run, packed, in a trench 1 ft 6 in wide. Behind it: 3.5 tons of clean stone, 1 ft thick.
- Blocks and caps cost about $913 to $1,300. The stone is about $171 to $384. Delivery is extra.
- The blocks weigh about 3.0 tons.
Text this to a block dealer
Hi! For a retaining wall I need about 80 wall blocks (8 x 18 in face), 20 caps, 0.9 tons of crusher run and 3.5 tons of 3/4 in clean stone. What would it cost, with delivery?
How tall can a block wall be?
Without reinforcement and an engineer, a short block wall leans on its own weight. Makers say how tall that can be. The height counts the buried row.
| Block | Ground behind | Tallest wall |
|---|---|---|
| Large, 8 × 18 in | Clay | 3 ft 2 in97 cm |
| Large, 8 × 18 in | Silty sand | 4 ft 7 in140 cm |
| Large, 8 × 18 in | Sand or gravel | 5 ft 2 in157 cm |
| Medium, 6 × 16 in | Any | about 3 ftabout 90 cm |
| Small, 4 × 12 in | Any | 2 ft60 cm |
A slope, a driveway or a building above the wall changes all of this. So do earthquake areas. Then a local engineer must design the wall.
Large block: Allan Block manual (2023), Table 1.3, AB Classic on level ground. Smaller blocks: Keystone FAQ. Other brands differ. Check the maker's chart for your block.
How to build the base
- Dig a trench. 24 in60 cm wide. For a wall under 4 ft1.2 m, 18 in46 cm wide is enough.
- Put down packed stone. At least 6 in15 cm (4 in10 cm for a wall under 4 ft1.2 m). Pack it flat.
- Bury the first row. 1 inch for every foot2.5 cm for every 30 cm of wall height. We count one whole row in the ground.
- Fill behind with clean stone. 12 in30 cm thick, all the way up. Fill the block holes too.
- Add a drain pipe behind the bottom row if the wall is over 4 ft1.2 m, or the ground stays wet.
How the math works
- Blocks in a row. Wall length in inches divided by the block's face length, rounded up.
- Rows. Wall height divided by the block's face height, rounded up, plus the buried row.
- Blocks. Rows times blocks in a row. Caps: one row on top. Buy a few spare blocks for cuts.
- Too tall? The rows times the block height is the full height. If it is more than the maker's limit, or there is a load above, we stop.
- Base stone. Trench width times length times the stone depth. It is crusher run, packed, so we add 1 / 0.89 (Caterpillar). Weight as on our gravel page.
- Wall rock. 12 in thick, full height, times the length. Clean #57 stone. The stone in the block holes is not counted, so buy a little more.
- Prices. What dealers post for each block size and for caps, the middle 80%. Caps: $8.87 to $13.23. Small plain blocks: only 4 dealers, so low to high. Stone: what yards post a ton, moved by your state's quarry price.
Questions
How many blocks do I need for a retaining wall?
Blocks in a row = wall length ÷ block length. Rows = wall height ÷ block height, plus one buried row. For a wall 30 ft long and 2 ft tall in 8 × 18 in block: 20 blocks a row, 4 rows, 80 blocks and 20 caps.
How much does a block retaining wall cost?
Large 8 × 18 in blocks cost about $9.20 to $12.95 each, and each covers about 1 sq ft of wall face. Caps cost $8.87 to $13.23. Add the gravel and delivery. Labor is extra if you hire it out.
How tall can I build a retaining wall myself?
With large blocks on level ground, Allan Block's chart goes from 3 ft 2 in in clay to 5 ft 2 in in sand or gravel, counting the buried row. Small 4 in blocks: about 2 ft. A slope or a driveway above: ask an engineer.
How much gravel goes behind a retaining wall?
A layer of clean stone 12 inches thick, the full height of the wall, says Allan Block. For a wall 30 ft long and 32 in tall, that is about 3.0 cubic yards.
How deep should a retaining wall be buried?
1 inch for every foot of wall height, plus 6 inches of packed stone under it, says Allan Block. We count one whole row of block in the ground.
Sources
- Allan Block, residential installationseen Oct 2026Trench, base, buried row, wall rock, drain pipe
- Allan Block commercial manual, Table 1.32023How tall a large-block wall can be, by soil
- Keystone Walls FAQseen Oct 2026How tall small blocks can go
- Caterpillar earthwork tablesJan 2025How much stone packs down