How Many Retaining Wall Blocks Do I Need? Quick Math
How many retaining wall blocks do I need comes down to two numbers: the face area of the wall and the face area of one block. Multiply wall length by wall height, including the buried course, then divide by the block’s exposed face. A common 12-inch-long by 4-inch-tall garden block covers 1/3 square foot, so you need 3 blocks per square foot. A larger 16 by 6 inch block covers 2/3 square foot, about 1.5 blocks per square foot. Then add caps and 5 to 10 percent for cuts.
Volume and tonnage calculator →Step-by-step count
- Wall length in feet along the face (measure curves along the front edge).
- Total height including the buried course.
- Face area = length × height.
- Blocks = face area ÷ block face area.
- Caps = wall length ÷ cap length.
- Add 5 to 10 percent for cuts, corners, and breakage.
Blocks per square foot by size
| Block face (L x H) | Face area | Blocks per sq ft |
|---|---|---|
| 12 x 4 in | 0.33 sq ft | 3.0 |
| 11.5 x 3 in (small edger-style) | 0.24 sq ft | 4.2 |
| 16 x 6 in | 0.67 sq ft | 1.5 |
| 18 x 6 in | 0.75 sq ft | 1.33 |
| 18 x 8 in (large) | 1.0 sq ft | 1.0 |
Check the exact face size on the manufacturer’s sheet; nominal sizes can differ.
Example: 30-foot wall, 3 feet tall
Using 16 x 6 inch blocks with one buried course:
- Height with buried course: 36 + 6 = 42 inches = 3.5 ft
- Face area: 30 × 3.5 = 105 sq ft
- Blocks: 105 × 1.5 = 158 blocks
- Add 7 percent: about 169 blocks
- Caps (12-inch caps): 30 caps, plus a few spares
That is 7 courses of about 22.5 blocks each, rounded up.
Curves and corners
Inside curves use slightly fewer blocks along the front because the faces squeeze together; outside curves use more and often need splitting. Corners need special corner blocks or cut blocks. Add the higher end of the waste range for walls with many curves.
Weight and delivery
Blocks are heavy. A 16 by 6 inch block often weighs 30 to 40 pounds, so 170 blocks can weigh 3 tons. Ask how many come on a pallet and whether the truck can place pallets close to the wall. See retaining wall block weight.
Do not forget the base and gravel
Every block wall needs a compacted base and drainage stone. For a 30-foot wall, plan on roughly 1.5 tons of base and 3 to 4 cubic yards of drainage stone, depending on wall height. See retaining wall base gravel.
Bottom line
To count retaining wall blocks, multiply length by total height including the buried course, divide by one block’s face area, add caps, and add 5 to 10 percent. With 16 by 6 inch blocks, that is about 1.5 blocks per square foot of wall face.
Questions people ask
How many retaining wall blocks per square foot?
About 3 for a 12 by 4 inch block, 1.5 for a 16 by 6 inch block, and 1 for an 18 by 8 inch block.
How many blocks do I need for a 3-foot retaining wall?
For a 30-foot wall with 16 by 6 inch blocks and one buried course, about 160 to 170 blocks.
Should I count the buried course?
Yes. Most walls bury the first course partly or fully, so include it.
How many cap blocks do I need?
Divide wall length by cap length and add a few spares for cuts.
How much extra should I order?
About 5 percent for straight walls and up to 10 percent for walls with curves and corners.
Related guides
- Retaining Wall Base Gravel: Type, Depth, and Tons
- Retaining Wall Block Weight: Sizes, Pallets, and Loads
- How Much Concrete for a Retaining Wall Footing?
- Crushed Stone for Retaining Wall Backfill
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