Hardscape calculator
Retaining wall block calculator
Enter the wall length, exposed height and block size to get the course count, total blocks including buried courses, capstones, leveling pad gravel and drainage stone.
Your project
Height above finished grade. Buried courses are added automatically.
Wall blocks to order
170
7 courses × 23 per course · 5% waste
- Total wall height
- 3.5 ft (incl. buried)
- Buried courses
- 1
- Capstones
- 23
- Leveling pad gravel (6")
- 1.69 tons
- Drainage backfill (12" chimney)
- 5.25 tons
- Drainage backfill by volume
- 3.89 cu yd
- Wall face area
- 90 sq ft
- Installed cost range
- $2,250 – $5,850
Bury one full course (or 10% of wall height, whichever is greater), set it on 6" of compacted crushed base, and keep a 12" chimney of clean drainage stone with a perforated drain tile behind the wall face.
How the block count is derived
Blocks per course is wall length in inches divided by block face length. Course count is total wall height divided by block height — and total height is not the height you see, because the bottom course is buried.
The rule is one full buried course, or 10% of the finished height, whichever is greater. A 4 ft wall built with 6" block therefore needs 9 courses, not 8. Skipping the buried course is why cheap walls lean forward within two winters.
A 5% breakage allowance is included. Blocks split during handling, and corner or curve work consumes extra units that cannot be recovered from offcuts.
Drainage is structural, not optional
The 12 inch chimney of clean #57 stone behind the wall face lets water reach a perforated drain tile at the base instead of loading the wall with hydrostatic pressure. Saturated soil behind a wall can more than double the lateral load the blocks were designed for.
Wrap the drainage zone in non-woven geotextile so fines from the retained soil do not migrate in and clog the stone. Daylight the drain tile at both ends where possible.
Any wall over 4 feet of exposed height, or any wall with a slope, driveway or structure surcharging it, needs an engineered design with geogrid reinforcement extending back into the retained soil.
Blocks per course by block size
Per 10 linear feet of wall, before waste.
| Block | Face length | Blocks / 10 ft | Courses per foot of height |
|---|---|---|---|
| 12" x 4" x 8" garden wall block | 12" | 10 | 3 |
| 12" x 6" x 8" standard block | 12" | 10 | 2 |
| 16" x 6" x 10" retaining block | 16" | 8 | 2 |
| 18" x 8" x 12" large block | 18" | 7 | 1.5 |
Wall height requirements
| Exposed height | Buried courses | Typical requirement |
|---|---|---|
| Under 2 ft | 1 | No permit in most jurisdictions, no geogrid |
| 2 - 3 ft | 1 | Compacted base and drainage chimney essential |
| 3 - 4 ft | 1 | Check local permit threshold before building |
| Over 4 ft | 1 minimum, often 2 | Engineered design, geogrid, permit and inspection |
| Any height with a surcharge | Per engineer | Driveway, slope or structure above requires design |
Frequently asked questions
+How many retaining wall blocks do I need?
Multiply blocks per course (wall length in inches ÷ block face length) by course count (total wall height in inches ÷ block height), then add 5% for breakage. Remember total height includes at least one buried course.
+How deep should the first course be buried?
One full course, or 10% of the finished wall height — whichever is greater. That buried course sits on 6 inches of compacted crushed base and resists the wall being pushed forward at its weakest point.
+How much gravel do I need behind a retaining wall?
A 12 inch wide chimney of clean #57 drainage stone running the full height and length of the wall. For a 30 ft × 3 ft wall that is roughly 3.5 cubic yards, or about 4.7 tons.
+Do I need geogrid?
Generally for anything above 4 feet exposed, or any height with a slope, driveway or structure loading the soil behind it. Geogrid layers extend back into the retained fill and turn the soil mass itself into part of the structure.
+How many capstones do I need?
One course worth — the same count as any other course, unless your cap unit has a different face length. Caps are glued down with concrete adhesive, not stacked dry.
+What does a retaining wall cost per square foot?
Segmental block walls run $25 – $65 per square foot of wall face installed. Cost per square foot rises with height because deeper base, geogrid and engineering all get added.