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Retaining Wall Calculator

Blocks, caps, base and drainage stone, and drain pipe for a segmental retaining wall, plus the dig and the delivery.

Quick answer

A 30 ft wall standing 2 ft tall in 8 x 18 in block takes 4 courses (one buried) of 20: 84 blocks with 5 percent extra, 20 caps, and about 4.9 tons of clean crushed stone for the base and the 12 in behind the block. The blocks alone weigh about 6,400 lb.

Measure the wall

Along the face

The buried course is added

Block

From your supplier

Cuts and chips

Also needed on wet or clay sites

84 blocks and 4.9 tons of stone.

For a 30 ft wall, 2 ft above ground

84blocks

4.9tons of stone

1.8pallets

4 courses (1 buried) of 20 · 20 caps · about 16,300 lb

The wall is 32 in of block from the base up: 3 courses show and 1 sits below grade. Stone fills a 18 x 4 in base and 12 in behind the block, per the Allan Block guide.

HaulOnce order ticket

Retaining wall

Ticket no.

562519

Wall block, 8 x 18 in face, with 5% extra84
Cap units20
3/4 in clean crushed stone (wall rock)4 cu yd
Of that: base / behind the block0.56 / 2.96 cu yd
Construction adhesive for the capsyes
Pallets of block1.75
Weight to haul (block and stone)16,278 lb

Example price, enter yours

Example price

Example price

Example price

Materials total$826
Per square foot of wall face$13.76

Materials only. Filter fabric, adhesive, delivery, and a plate compactor rental are extra.

Estimate from haulonce.com. Weights vary with moisture and supplier. Prices are examples unless you entered your own.

The dirt you dig out

The base trench is 18 in wide and 12 in deep: 1.7 cu yd in the ground, about 2.1 cu yd once it is dug and fluffed up, weighing 3,300 to 4,500 lb. Most of it can go back as backfill behind the stone. Cutting into a slope digs out more.

A few pickup loads, or offer it free online as clean fill. Soil is heavy, so check payload before loading.

Haul Check

Typical 1,150 to 2,400 lb. We use the low end until you enter yours.

Check the Tire and Loading Information sticker on your driver's door jamb for your exact payload.

Payload16,278 of 1,150 lb (1,415%)

That is 15,128 lb over your payload. Plan on 15 trips of about 1,085 lb.

At this many trips, ask the yard what delivery costs. It is often less than your time and fuel.

Using the low end of the typical payload range. Enter your own for an exact answer.

What pros know

  • The base makes the wall. Dig the trench, compact the soil, then lay and compact at least 6 in of crushed stone before the first block. Source
  • Bury the first course, plus about 1 in for every foot of wall height. Source
  • Fill 12 in behind the block with clean crushed stone so water drains instead of pushing on the wall. Source
  • Over 4 ft tall, a retaining wall usually needs an engineer, and often a permit. Check with your town first. Source

Pricing the stone on its own? The #57 stone calculator does bags or bulk and truck trips.

Ready to text or email your supplier:

“Retaining wall: 84 wall blocks (8 x 18 in face), 20 caps, 4 cu yd of 3/4 in clean crushed stone.”

84 blocks · 4.9 t stoneSee list

How many retaining wall blocks do I need?

Count courses, then blocks per course. Divide the height above ground by the block height and round up, then add the buried course: at least one full course goes below grade, plus about 1 in for every foot of wall height (Allan Block). Divide the wall length by the block's face length for the blocks in each course, and multiply.

Per square foot of face, a 4 x 12 in block works out to about 3.1 blocks and an 8 x 18 in block to 1. Caps run the length of the top course.

Large wall block, 8 x 18 in face: blocks to buy including the buried course and 5 percent extra, not counting caps.
Height above ground10 ft long20 ft long30 ft long50 ft long
1 ft234563108
2 ft305984143
3 ft4589126215
4 ft52103147250
Small wall block, 4 x 12 in face: blocks to buy including the buried course and 5 percent extra, not counting caps.
Height above ground10 ft long20 ft long30 ft long50 ft long
1 ft4789131219
2 ft81155228383
3 ft116221326546
4 ft151287424710

Base, drainage stone, and drain pipe

Allan Block's install guide digs a trench 24 in wide with 6 in of compacted wall rock (clean crushed stone) under the first course; for walls under 4 ft, 18 in wide and 4 in deep. Add the buried block to the trench depth.

Behind the block, fill 12 in with the same stone for the full height, so water drains down instead of pushing on the wall. A 4 in perforated drain pipe at the back of the base is required for walls over 4 ft and on poorly drained ground, with an outlet to daylight at least every 50 ft. The calculator totals the stone in cubic yards and tons; the #57 stone calculator compares bags and bulk.

How tall can a block wall be without an engineer?

The IRC calls for an engineered design when a retaining wall holds back more than 48 in of soil without support at the top, and many towns want a permit at a lower height, especially near property lines, driveways, or slopes. Block makers publish their own maximum heights for each block without geogrid, often lower for small garden blocks. Check both before you build, and call 811 before you dig.

What a retaining wall costs

Enter your block, cap, stone, and pipe prices for the materials total and a cost per square foot of wall face. The defaults are examples only. Installed prices add excavation, compaction equipment, delivery, and labor, so a contractor's quote will be well above the materials.

Getting it home

Wall block is about the heaviest thing a homeowner buys. An 8 x 18 in block runs about 76.5 lb, so a half-ton's 1,150 lb payload carries only 15 of them, and a pallet of 48 is about 3,700 lb. Add the stone and most walls are a delivery: ask for the pallets dropped close to the wall, since you will move every block by hand.

What pros know

  • The base makes the wall. Dig the trench, compact the soil, then lay and compact at least 6 in of crushed stone before the first block. (Allan Block)
  • Bury the first course, plus about 1 in for every foot of wall height. (Allan Block)
  • Fill 12 in behind the block with clean crushed stone so water drains instead of pushing on the wall. (Allan Block)
  • Over 4 ft tall, a retaining wall usually needs an engineer, and often a permit. Check with your town first. (International Code Council)

Common mistakes

  • Setting the first course on soil or sand instead of compacted crushed stone.
  • Forgetting the buried course, which leaves the wall a block short.
  • Backfilling with dirt right against the block instead of drainage stone.
  • Building taller than the block's limit without geogrid or an engineer.
  • Not leaving an outlet for the drain pipe, so it fills and does nothing.

Questions people ask

How many retaining wall blocks do I need?

Courses (height divided by block height, plus one buried) times blocks per course (length divided by block length). A 30 ft wall 2 ft tall in 8 x 18 in block is 4 x 20 = 80, or 84 with 5 percent extra.

How much gravel do I need behind a retaining wall?

Allan Block fills 12 in behind the block with clean crushed stone for the full height, plus the base. For a 30 ft wall 2 ft tall, about 3.5 cu yd (4.9 tons) in all.

How deep should a retaining wall base be?

At least 6 in of compacted crushed stone in a 24 in wide trench (4 in and 18 in wide for walls under 4 ft), plus the depth of the buried course.

How tall can a retaining wall be without a permit?

The IRC requires an engineered design past 48 in of retained soil, and many towns require a permit lower than that. Check with your building department.

How many retaining wall blocks are on a pallet?

It depends on the size: one retail listing puts 144 small 4 x 12 in blocks on a pallet, and one producer ships 48 of the 8 x 18 in size.

Sources

Last reviewed: . How we calculate

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