How many retaining wall blocks do I need?

Divide the wall's length by the block's face length for the blocks per course, and the height by the block's height for the courses, rounding both up, then add the buried course. A 30 ft wall 3 ft high of 6 × 16 in blocks is 23 blocks × 6 courses above ground + 1 buried = 161 blocks, and 23 caps.

How many retaining wall blocks per square foot?

It depends on the face: 144 ÷ (height × length in inches). Versa-Lok's 4 × 12 in unit lays 3.00, the 6 × 16 in unit lays 1.50, the 8 × 18 in unit lays 1.00 per sq ft of face, before the buried course and the cut blocks at the ends.

How deep should a retaining wall base be?

Allan Block asks for a trench 24 in wide with at least 6 in of compacted wall rock, or 18 in wide with 4 in for a wall under 4 ft, with the first course buried at least 6 in. Your block maker's guide and plans set the base for your wall.

How much gravel do I need for a retaining wall base?

For the 30 ft wall on an 18 × 4 in base, 15.00 cu ft compacted, about 1.03 tons of base gravel to order with 20% for compaction. The calculator weighs it as base gravel; Allan Block's wall rock is a compactible aggregate of 1/4 to 1 1/2 in with under 10% fines.

How much drainage gravel goes behind a retaining wall?

At least 12 in behind the block and in its cores, by Allan Block. For the 30 ft wall built 3.5 ft high, buried course included, that is 3.89 cu yd behind the blocks, about 6.03 tons of #57 stone; the cores take a little more. A drain pipe is required over 4 ft or in silty or clay soil.

How many cap blocks do I need?

The wall's length ÷ the cap's length, rounded up: 23 caps of 16 in for a 30 ft wall. Caps come in their own sizes, so type yours; on a curved wall or with corner caps, count a few extra for cuts.

How tall can a block retaining wall be without an engineer?

Fixr advises a structural engineer for walls over 4 ft, and your local building department says from what height a wall needs a permit. Each block maker also sets the height its blocks can stand without geogrid; check its chart for your block and soil.

How much does a retaining wall block cost?

About $6–$11 a block, by Inch Calculator (updated August 6, 2023), and an installed segmental wall runs $15–$35 per square foot of face, by Fixr. The calculator starts with example prices of $5 a block and $4 a cap: type your store's.

Retaining Wall Block Calculator

A landscape retaining wall 30 ft long and 3 ft high of 6 × 16 in blocks takes 161 blocks, 23 per course in 7 courses with one course buried, and 23 caps on top. Enter the wall's length and its height above ground and pick a block to get the blocks and caps, the gravel base in the trench, the drainage gravel behind the wall in cubic yards and tons, and the cost at your block price.

Units

Wall lengthWall height above ground

Block face (height × length)

Block height (in)Block length (in)Cap length (in)Buried depth (in)

Presets: Versa-Lok's Accent (4 × 12 in), Standard (6 × 16 in), Square Foot (8 × 18 in) units. Other brands differ, so type the face of yours; a cap length of 0 leaves the caps out.

Gravel base (Allan Block)

Trench width (in)Base depth (in)Drainage gravel behind (in)

Price per block ($)Price per cap ($)

161 blocks and 23 caps

Wall face above ground:: 90.0 sq ft
Courses × blocks per course:: 7 × 23 (1 buried course, 6 courses above ground)
Gravel base, base gravel (crusher run, #411, ABC) with 20% for compaction:: 0.67 cu yd (18.00 cu ft), about 1.03 tons
Drainage gravel behind the wall, #57 or 3/4 in crushed stone:: 3.89 cu yd (105.00 cu ft), about 6.03 tons
Blocks and caps at your prices:: $897 ($9.97 per sq ft of face)

Example prices only: type your store's. Base gravel and #57 stone weighed at the middle of their published ranges.

A mortared cinder block wall instead? Count it in the concrete block calculator.
Its installed price: the block wall cost calculator.
A poured concrete retaining wall and its footing: the concrete wall calculator.

How HomeMath counts retaining wall blocks

HomeMath counts by course. Blocks per course are the wall's length ÷ the block's face length, rounded up; the courses are the height above ground ÷ the block's height, rounded up, plus the buried courses that reach the buried depth (Allan Block asks for at least 6 in). Blocks = courses × blocks per course, and caps = the length ÷ the cap's length, rounded up. The base is the trench's length × width × the base depth, with 20% added for compaction, weighed as base gravel. The drainage gravel is the length × 12 in × the built height, buried course included, weighed as #57 stone, at the middle of each published range. Dry-stacked blocks have no mortar joint, so the face is the block's own size. In metric, HomeMath converts meters and centimeters exactly (1 in = 2.54 cm) and shows the result in cubic meters, liters and square meters.

The published rules it uses: segmental retaining walls; US customary units; metric conversion; gravel weights and prices. Their sources, and how HomeMath tests every result, are on the about page.

How many blocks do common retaining walls take?

Blocks include the buried course; caps run the wall's length.

Garden bed 12 ft × 1 ft, 4 × 12 in blocks60 blocks · 12 caps
Garden wall 20 ft × 2 ft, 6 × 16 in blocks75 blocks · 15 caps
Yard wall 30 ft × 3 ft, 6 × 16 in blocks161 blocks · 23 caps
Yard wall 50 ft × 3 ft, 8 × 18 in blocks204 blocks · 34 caps
Slope wall 40 ft × 4 ft, 8 × 18 in blocks189 blocks · 27 caps

How do I count retaining wall blocks by hand?

Blocks per course: 30 ft × 12 = 360 in ÷ 16 in = 22.5, so 23.
Courses above ground: 3 ft × 12 = 36 in ÷ 6 in = 6, plus 1 buried course for the 6 in below ground: 7.
Blocks: 7 × 23 = 161; caps: 360 ÷ 16 rounded up = 23. On a curved wall or with corner caps, add a few for cuts.
At example prices of $5 a block and $4 a cap: $897.

How many blocks does each foot of wall take?

The calculator's presets are Versa-Lok's Accent, Standard and Square Foot units, 4 × 12 in, 6 × 16 in, 8 × 18 in on the face. Other brands use other faces, so type yours. Blocks per foot of length, buried course included:

Blocks per foot of wall length, by height above ground
Block face	1 ft	2 ft	3 ft	4 ft
4 × 12 in (Versa-Lok Accent)	5.0	8.0	11.0	14.0
6 × 16 in (Versa-Lok Standard)	2.3	3.8	5.3	6.8
8 × 18 in (Versa-Lok Square Foot)	2.0	2.7	4.0	4.7

How wide and deep should the base of a retaining wall be?

Allan Block's gravity wall construction sets the base: a trench 24 in wide with at least 6 in of compacted wall rock, or 18 in wide with 4 in for a wall under 4 ft, and at least 6 in of buried block. The calculator has both bases as presets. Your block maker's guide and plans set the base for your wall.

How much base and drainage gravel does 10 ft of wall need?

Allan Block fills the block cores and at least 12 in behind the wall with wall rock, a compactible stone that lets water drain, and requires a drain pipe for walls over 4 ft or in silty or clay soil. The table uses the base for the wall's height and 12 in of stone behind the built height, buried course included, for 6 × 16 in blocks. The base is weighed as base gravel (crusher run, #411 or ABC) with 20% added for compaction, the drainage stone as #57; the block cores take a little more.

Base and drainage gravel per 10 ft of wall
Height above ground	Base gravel to order	Drainage gravel
1 ft (18 × 4 in base)	6.00 cu ft, 0.34 tons	15.00 cu ft, 0.86 tons
2 ft (18 × 4 in base)	6.00 cu ft, 0.34 tons	25.00 cu ft, 1.44 tons
3 ft (18 × 4 in base)	6.00 cu ft, 0.34 tons	35.00 cu ft, 2.01 tons
4 ft (24 × 6 in base)	12.00 cu ft, 0.69 tons	45.00 cu ft, 2.58 tons

The 30 ft wall above takes 3.89 cu yd of drainage stone. For any other gravel job, the gravel calculator gives yards, tons and cost.

Is a cinder block retaining wall the same job?

No. Landscape blocks stack without mortar and lock with a lip or pins, so a low wall is a common DIY job. A cinder block retaining wall is laid in mortar on a poured footing, usually with rebar and filled cores: size its footing in the concrete wall calculator, count its blocks in the concrete block calculator and price it installed in the block wall cost calculator. Fixr advises a structural engineer for any retaining wall over 4 ft. Which block types suit a structural wall is in our guide to concrete block types.

What do retaining wall blocks cost?

Inch Calculator puts a retaining wall block at $6–$11 (updated August 6, 2023), and Fixr an installed segmental wall at $15–$35 per square foot of face, labor included (updated January 31, 2025). The price fields start with round example numbers; type your store's prices for the blocks and the caps.

Frequently asked questions

How many retaining wall blocks do I need?: Divide the wall's length by the block's face length for the blocks per course, and the height by the block's height for the courses, rounding both up, then add the buried course. A 30 ft wall 3 ft high of 6 × 16 in blocks is 23 blocks × 6 courses above ground + 1 buried = 161 blocks, and 23 caps.
How many retaining wall blocks per square foot?: It depends on the face: 144 ÷ (height × length in inches). Versa-Lok's 4 × 12 in unit lays 3.00, the 6 × 16 in unit lays 1.50, the 8 × 18 in unit lays 1.00 per sq ft of face, before the buried course and the cut blocks at the ends.
How deep should a retaining wall base be?: Allan Block asks for a trench 24 in wide with at least 6 in of compacted wall rock, or 18 in wide with 4 in for a wall under 4 ft, with the first course buried at least 6 in. Your block maker's guide and plans set the base for your wall.
How much gravel do I need for a retaining wall base?: For the 30 ft wall on an 18 × 4 in base, 15.00 cu ft compacted, about 1.03 tons of base gravel to order with 20% for compaction. The calculator weighs it as base gravel; Allan Block's wall rock is a compactible aggregate of 1/4 to 1 1/2 in with under 10% fines.
How much drainage gravel goes behind a retaining wall?: At least 12 in behind the block and in its cores, by Allan Block. For the 30 ft wall built 3.5 ft high, buried course included, that is 3.89 cu yd behind the blocks, about 6.03 tons of #57 stone; the cores take a little more. A drain pipe is required over 4 ft or in silty or clay soil.
How many cap blocks do I need?: The wall's length ÷ the cap's length, rounded up: 23 caps of 16 in for a 30 ft wall. Caps come in their own sizes, so type yours; on a curved wall or with corner caps, count a few extra for cuts.
How tall can a block retaining wall be without an engineer?: Fixr advises a structural engineer for walls over 4 ft, and your local building department says from what height a wall needs a permit. Each block maker also sets the height its blocks can stand without geogrid; check its chart for your block and soil.
How much does a retaining wall block cost?: About $6–$11 a block, by Inch Calculator (updated August 6, 2023), and an installed segmental wall runs $15–$35 per square foot of face, by Fixr. The calculator starts with example prices of $5 a block and $4 a cap: type your store's.