Retaining Wall Calculator
Blocks, caps, base stone and drainage — with the installed cost per face square foot.
Blocks to order
200
- Face area
- 120 sq ft
- Courses
- 5
- Blocks per course
- 40
- Wall blocks
- 200
- Cap blocks
- 40
- Base stone
- 1.78 yd³
- Drainage stone
- 4.44 yd³
- Blocks
- $680.00
- Caps
- $220.00
- Stone
- $298.67
- Drain pipe
- $72.00
- Labor
- $2,640.00
- Contingency (10%)
- $391.07
- Total
- $4,301.73
- Per face sq ft
- $35.85/sq ft
- Material-only (DIY)
- $1,270.67
Courses round up: a wall 3 ft high in 8 in block is 4.5 courses, so you buy 5.
Pricing the base and drainage stone on its own? Use the gravel calculator →
How this is calculated
courses = ceil(height × 12 ÷ block height) blocks/course = ceil(length × 12 ÷ block face) wall blocks = courses × blocks per course caps = blocks per course base stone yd³ = length × trench width × base depth ÷ 27 × 1.20 drainage yd³ = length × stone width × wall height ÷ 27 total = (blocks + caps + stone + pipe + labor) × (1 + contingency%)
Base stone carries a 20 percent compaction allowance — crushed stone loses roughly that much volume once it is plate-compacted, and ordering the loose volume leaves you short. Drainage stone behind the wall is not compacted, so it takes no allowance.
Blocks by wall size
Standard 12 inch face by 8 inch high block. Same function as the calculator above.
| Wall | Face area | Courses | Blocks | Caps |
|---|---|---|---|---|
| 20 ft × 2 ft | 40 sq ft | 3 | 60 | 20 |
| 20 ft × 3 ft | 60 sq ft | 5 | 100 | 20 |
| 30 ft × 3 ft | 90 sq ft | 5 | 150 | 30 |
| 40 ft × 3 ft | 120 sq ft | 5 | 200 | 40 |
| 40 ft × 4 ft | 160 sq ft | 6 | 240 | 40 |
| 50 ft × 4 ft | 200 sq ft | 6 | 300 | 50 |
Installed cost by wall type
| Wall type | Installed per face sq ft | Notes |
|---|---|---|
| Segmental block, under 3 ft | $25-$40 | No engineering in most areas |
| Segmental block, 3-4 ft | $30-$50 | Geogrid often required |
| Segmental block, over 4 ft | $45-$90 | Engineered design and permit |
| High-cost metro areas | $70-$260 | Coastal California and similar |
| Poured concrete | $40-$90 | Forms, steel and a pump |
| Natural stone | $40-$120 | Highly dependent on stone and mason |
| Treated timber | $18-$35 | Cheapest up front, 15-20 year life |
Frequently asked questions
How many blocks do I need for a retaining wall?
Divide the wall length by the block face length to get blocks per course, then the wall height by the block height to get the number of courses, and multiply. A 40 foot wall 3 feet high in standard 12 by 8 inch block needs 5 courses of 40 blocks, so 200 blocks, plus 40 caps.
How much does a retaining wall cost?
Installed segmental block walls generally run $25 to $60 per face square foot, so a 40 foot wall 3 feet high lands roughly $3,000 to $7,000. Material alone is about a third of that. Price climbs sharply past 4 feet, where engineering, geogrid reinforcement and permits usually enter the picture.
How deep should the base course be?
Bury the first course about one inch for every foot of wall height, with a minimum of one full course below finished grade. Under that sits 6 to 8 inches of compacted crushed stone in a trench twice the block depth. Nearly every failed wall traces back to base preparation, not to the blocks.
Do I need drainage behind the wall?
Yes, on anything holding real soil. Twelve inches of clean drainage stone against the back of the blocks, with a perforated pipe daylighting at one end, keeps water from building hydrostatic pressure. Water, not soil weight, is what pushes most residential walls over.
How tall can I build without an engineer?
Many jurisdictions require an engineered design and a permit above 4 feet, measured from the bottom of the base course. Slopes above the wall, driveways or structures near the top, and tiered walls can all lower that threshold. Check locally before buying material — this calculator does not model reinforcement.
What is geogrid and do I need it?
Geogrid is a stiff mesh laid between courses and extending back into the retained soil, tying the wall and the soil into one mass. Below 3 feet on level ground it is usually unnecessary; above 4 feet, or with any surcharge above the wall, it is normally required and its spacing comes from the engineer, not from a rule of thumb.
This estimates material and cost only. It does not size geogrid, check global stability or model surcharge from slopes, driveways or structures above the wall. Anything over 4 feet, or holding a slope, needs a licensed engineer and a permit.