Retaining wall block calculator: how many retaining wall blocks do I need?
60 blocks
40 square feet of surface · 15 more for 1 buried course · gravel: 0.75 cu yd base and 1.49 cu yd drainage stone · for 20 × 2 ft
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Enter it the way you measured it: 4.5, 4 1/2,
3/8 or 10' 6".
60 blocks
40 square feet of surface · 15 more for 1 buried course · gravel: 0.75 cu yd base and 1.49 cu yd drainage stone
Source: VERSA-LOK Standard Design & Installation Guidelines (VLS-602): embedment, leveling pad, drainage aggregate and the wall heights that need a drain pipe or an engineer, read November 9, 2026. Data sheet (PDF)
A 20 ft long, 2 ft high retaining wall takes 60 blocks with a 16 by 6 inch face, because that face covers 0.67 square feet. Change the face size to the block you are buying.
A worked example
A 30 ft long, 3 ft high wall in 12 by 8 in blocks, with a 5% waste allowance needs 142 blocks. 90 square feet of wall face, and a 12 by 8 in face covers 0.67 square feet, so 135 blocks plus the 5% allowance is 142.
How deep do you bury the first course of a retaining wall?
One-tenth of the height that shows above ground, per the VERSA-LOK installation guide, rounded up to a full course of block. A 2 ft wall needs 2.4 inches buried, so one course of 6 inch block goes below grade; a 10 ft wall needs a foot. Bury more where the ground slopes down in front of the wall or the soil is soft. The calculator above adds the buried blocks for your wall length and block height.
How much gravel do I need for a retaining wall?
Two loads of gravel, base and drainage. The leveling pad is at least 6 inches thick and 24 inches wide, so each 10 ft of wall takes 10 cubic feet, 0.38 cubic yards to order. Behind the blocks goes 3/4 inch clean angular stone at 1 cubic foot per square foot of exposed face, so a 20 by 2 ft wall takes 40 cubic feet, 1.49 cubic yards to order. Both figures are from the VERSA-LOK guide, and the calculator gives them for your wall in cubic yards, the way bulk gravel is sold.
What else it is called
Retaining wall blocks, also called segmental or SRW blocks, are sold by the block and by the pallet, with cap blocks and corner blocks as separate pieces. The face count depends on the face size you pick, not the brand. Below grade the wall needs more than the face: a buried course, a 6 by 24 inch gravel base and a foot of drainage stone behind it, all in the result above. VERSA-LOK rates its gravity walls stable to 3 to 4 feet on level backfill and good soil; taller walls take geogrid layers, and the calculator flags the heights where its guide calls for a drain pipe or an engineer.
Common sizes
| Area | 12 × 4 in face | 16 × 6 in face (VERSA-LOK Standard size) | 18 × 6 in face | 12 × 8 in face |
|---|---|---|---|---|
| 8 × 8 ft — 64 sq ft | 192 | 96 | 86 | 96 |
| 10 × 10 ft — 100 sq ft | 300 | 150 | 134 | 150 |
| 10 × 12 ft — 120 sq ft | 360 | 180 | 160 | 180 |
| 12 × 12 ft — 144 sq ft | 432 | 216 | 192 | 216 |
| 12 × 16 ft — 192 sq ft | 576 | 288 | 256 | 288 |
| 16 × 20 ft — 320 sq ft | 960 | 480 | 427 | 480 |
| 20 × 20 ft — 400 sq ft | 1200 | 600 | 534 | 600 |
Pieces, rounded up, with no waste allowance added.
Where the numbers come from
- A block covers its face, width times height: a 16 by 6 inch face is 0.67 square feet. The face count is the wall face area, length times height, divided by that coverage, rounded up, so it depends only on the block face you pick.
- Buried course, base and drainage stone: VERSA-LOK Standard Design & Installation Guidelines (VLS-602). «One-tenth of the exposed wall height should be buried (embedded) below grade», rounded here up to whole courses of your block; the «leveling pad should be at least 6 inches thick and 24 inches wide»; drainage aggregate goes behind the units at «a minimum of 1 cubic foot for each exposed square foot of wall face». For walls over 3 feet the guide calls for a perforated drain pipe, and «for walls more than 4 feet in height, most building codes require a final wall design prepared by a licensed, professional engineer». Read November 9, 2026. Read the VERSA-LOK installation guide (PDF)
- The VERSA-LOK Standard unit is 6 in high by 16 in wide by 12 in deep and weighs 82 lb, a face of 2/3 square foot, which is the 16 × 6 in option above. Read November 9, 2026. VERSA-LOK Standard sell sheet (PDF)
The buried course runs the full wall length at the block height you pick. Cap blocks for the top are a different piece, sold separately: count your wall length divided by the cap length. A curved or stepped wall cuts more, so raise the waste allowance.
By Javier Miralles · Last updated . How this site is made.
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