The Block CalculatorHow does this retaining wall block calculator work?
Enter the exposed length and height of the wall and the face size of one retaining wall block. The calculator returns the number of blocks for the wall face. Segmental retaining wall blocks are usually dry-stacked without mortar, so use the manufacturer’s actual face size.
What to add to your estimate
- Buried course: most systems bury the first course below grade. Add one block height to the wall height you enter.
- Cap units: capstones are sold separately; you need roughly the wall length divided by the cap length.
- Base and drainage: plan for a compacted gravel base, drainage aggregate behind the wall and a perforated drain pipe.
- Height limits: many local codes require an engineered design for retaining walls above about 4 ft (1.2 m) or walls with a surcharge such as a driveway. Check your local rules.
Formula used
Total Blocks = (Wall Length × Wall Height) ÷ (Block Length × Block Height)The result is always rounded up to the next whole block, because you can’t buy part of one. Wall thickness is shown in the diagram but does not change the count for a single-wythe wall.
Example
Scenario: A wall 10 m long and 2 m high, built with blocks measuring 40 cm × 20 cm (0.4 m × 0.2 m).
Wall area: 10 m × 2 m = 20 m²
Block face area: 0.4 m × 0.2 m = 0.08 m²
Final result: 20 ÷ 0.08 = 250 blocks. Add 5–10% for cuts and breakage when you order.
Frequently asked questions
Do retaining wall blocks need mortar?
Most segmental retaining wall blocks are dry-stacked and held by lips or pins, with adhesive on the top course. Always follow the manufacturer’s installation guide.
Should the buried course be included?
Yes. Add the buried course height to the exposed height so the calculator counts those blocks.
Last updated: . Results are estimates — see our disclaimer.