Retaining Wall Calculator
Calculate materials for retaining walls including blocks, gravel, drainage pipe, and geogrid. Supports segmental blocks, timber, and concrete walls.
Wall Type
Wall Dimensions
Block Size
18" x 6" face
Drainage & Reinforcement
Related Calculators
About This Calculator
Building a retaining wall requires careful material planning—from the blocks or timbers to the crucial drainage and reinforcement systems that prevent failure. Our Retaining Wall Calculator estimates all materials needed for segmental block walls, timber walls, and poured concrete walls, including blocks, backfill gravel, drainage pipe, filter fabric, and geogrid reinforcement.
Retaining walls hold back soil, creating level areas on sloped properties, preventing erosion, and maximizing usable yard space. But unlike decorative garden walls, retaining walls must resist constant lateral soil pressure that increases exponentially with height. A 4-foot wall experiences four times the pressure of a 2-foot wall, not twice. Underestimating materials or skipping drainage leads to bulging, cracking, and eventual collapse—often within just a few years.
In 2026, retaining wall costs range from $35-65 per square foot installed, or $40-345 per linear foot depending on height and materials. DIY materials-only costs run $10-30 per square foot. Enter your wall dimensions to get a complete materials list and cost estimate for your specific project.
Trusted Sources
How to Use the Retaining Wall Calculator
- 1Select your wall type (segmental block, timber, or poured concrete).
- 2Enter the total length and exposed height of your retaining wall.
- 3Specify the batter (setback) if your blocks step back on each course.
- 4Toggle drainage options (gravel backfill, perforated pipe, filter fabric).
- 5Enable geogrid reinforcement for walls over 3 feet tall.
- 6Review the complete materials list with quantities and cost estimates.
- 7Add 10% to block quantities for cutting, breakage, and future repairs.
2026 Retaining Wall Costs by Material
Current pricing for retaining wall construction, including materials and installation:
Cost per Square Foot (Installed):
| Material | DIY Materials | Professional Installed |
|---|---|---|
| Interlocking Block (SRW) | $10-20/sf | $35-55/sf |
| Concrete Block (CMU) | $15-25/sf | $40-65/sf |
| Timber/Railroad Ties | $8-15/sf | $25-45/sf |
| Natural Stone | $25-50/sf | $55-100/sf |
| Poured Concrete | $20-35/sf | $45-75/sf |
| Boulder | $20-40/sf | $50-85/sf |
Cost per Linear Foot by Height:
| Wall Height | Interlocking Block | Timber | Poured Concrete |
|---|---|---|---|
| 2 ft | $45-90/lf | $35-70/lf | $55-110/lf |
| 3 ft | $70-140/lf | $50-100/lf | $85-170/lf |
| 4 ft | $95-190/lf | $70-140/lf | $115-230/lf |
| 6 ft | $145-290/lf | N/A (engineer req) | $175-350/lf |
Popular Block Prices (2026):
| Product | Price | Coverage |
|---|---|---|
| Pavestone SplitRock | $4.50-6.00/block | 0.33 sf face |
| Allan Block AB | $6-9/block | 0.5 sf face |
| Versa-Lok Standard | $5-8/block | 0.35 sf face |
| Belgard Anchor Diamond | $5-7/block | 0.4 sf face |
| Keystone Standard | $6-8/block | 0.5 sf face |
Prices vary by region. Expect 10-20% higher in coastal and urban areas.
Retaining Wall Types Compared
Choosing the right wall type depends on height, soil conditions, budget, and aesthetics:
Segmental Retaining Wall (SRW) Blocks:
- Interlocking concrete blocks with built-in setback
- DIY-friendly up to 3-4 feet
- No mortar required (dry-stack)
- Lifespan: 50-100 years with proper drainage
- Best for: Most residential applications
Timber/Landscape Ties:
- Pressure-treated lumber (6x6 or larger)
- Natural appearance suits woodland settings
- Easiest material to work with
- Lifespan: 15-25 years (rotting is inevitable)
- Best for: Budget projects, gentle slopes, temporary solutions
Poured Concrete:
- Strongest option pound-for-pound
- Requires forms, rebar, and often professional help
- Can be faced with stone or stucco
- Lifespan: 50+ years
- Best for: Commercial, tall walls, heavy surcharges
Natural Stone:
- Beautiful, timeless appearance
- Requires skilled mason for dry-stack
- Mortared stone is strongest
- Lifespan: 100+ years (essentially permanent)
- Best for: High-visibility areas, upscale properties
Boulder/Rip-Rap:
- Large natural rocks stacked by excavator
- Very fast installation
- Irregular appearance
- Lifespan: Permanent
- Best for: Rural settings, erosion control, streambanks
Height Limitations (DIY without engineer):
| Wall Type | Max DIY Height | When to Hire Engineer |
|---|---|---|
| Segmental blocks | 3-4 ft | Over 4 ft or surcharge |
| Timber | 3 ft | Over 3 ft |
| Poured concrete | 2-3 ft | Over 3 ft |
| Boulder | 2-3 ft | Over 3 ft or near structures |
Many jurisdictions require permits for walls over 3-4 feet. Always check local codes.
Critical Drainage Requirements
Water is the #1 cause of retaining wall failure. Proper drainage is absolutely non-negotiable:
The Complete Drainage System:
1. Gravel Backfill (12-24" behind wall):
- Clean crushed gravel, 3/4" minus or #57 stone
- 1 ton covers approximately 12 linear feet at 12" depth
- Never use native soil directly against wall back
- Cost: $45-65 per ton delivered
2. Perforated Drain Pipe (at base):
- 4" diameter perforated PVC or corrugated
- Holes facing DOWN toward gravel bed
- 1% minimum slope to outlet point
- Wrap in filter fabric sock
- Cost: $0.50-1.50 per foot
3. Filter Fabric (geotextile):
- Prevents soil migration into gravel
- Wrap completely around drain pipe
- Line back of excavation before gravel
- Overlap seams 12" minimum
- Cost: $0.15-0.50 per square foot
4. Drainage Outlet:
- Daylight to grade at lowest point
- Pop-up emitters or solid pipe to storm drain
- Never dead-end the drain pipe
- Cost: $15-30 per outlet
Backfill Material Requirements by Wall Height:
| Wall Height | Gravel Zone Width | Gravel per Linear Foot |
|---|---|---|
| 2 feet | 12" | 0.07 cu yd / 0.1 ton |
| 3 feet | 12-18" | 0.12 cu yd / 0.15 ton |
| 4 feet | 18-24" | 0.22 cu yd / 0.3 ton |
| 6 feet | 24"+ | Per engineer specs |
Why Drainage Matters (The Math):
- Dry soil lateral pressure: ~30 psf per foot of depth
- Saturated soil pressure: ~45-50 psf per foot
- Hydrostatic pressure adds: ~62.4 psf per foot of water height
- Combined pressure increase: 100-150% over dry conditions
Geogrid Reinforcement Guide
For walls over 3-4 feet, geogrid creates a "reinforced soil mass" that dramatically increases stability by tying the wall face to compacted soil behind it:
What is Geogrid? High-strength polymer mesh that grips soil through friction and interlock. Think of it as rebar for dirt—it converts the soil behind the wall into part of the structural system.
When to Use Geogrid:
| Wall Height | Geogrid Required? | Number of Layers |
|---|---|---|
| Under 2 ft | Not needed | 0 |
| 2-3 ft | Optional/Recommended | 0-1 |
| 3-4 ft | Recommended | 1-2 |
| 4-6 ft | Required | 2-3 |
| 6+ ft | Required (engineered) | 3-4+ |
Geogrid Installation Requirements:
| Application | Grid Length | Vertical Spacing |
|---|---|---|
| Light duty (residential) | 4 ft | Every 16-24" (2-3 courses) |
| Standard | 6 ft | Every 16" (2 courses) |
| Heavy duty/surcharge | 8-10 ft | Every 8-16" (1-2 courses) |
Installation Steps:
- Place first grid layer after 2-3 courses
- Lay grid perpendicular to wall face on compacted soil
- Roll back 6" and secure under next block course
- Backfill over grid in 6-8" lifts, compact each lift
- Repeat at specified vertical intervals
Geogrid Costs (2026):
| Product | Roll Size | Price |
|---|---|---|
| Tensar BX1100 | 4'x150' | $180-240 |
| Mirafi HP370 | 6'x150' | $280-360 |
| Stratagrid SG350 | 4'x250' | $220-300 |
| ACEGrid GG40-II | 6'x300' | $350-450 |
Geogrid adds $0.50-1.50 per square foot of wall face—minimal cost for preventing $10,000+ failures.
Wall Footing and Base Preparation
A proper base is essential—without it, your wall will settle, tilt, and fail regardless of how well you stack the blocks:
Base Course Preparation Steps:
1. Excavate Trench:
- Width: Block depth + 6-12" front + 18-24" back for drainage
- Depth: 6-8" below grade + height of buried course(s)
- Extend beyond wall ends 12" minimum
- Remove all organic material
2. Install Base Material:
- 6" compacted crushed stone (3/4" minus or process gravel)
- Compact in 3" lifts with plate compactor
- Level within 1/8" over 10 feet
- Extend base 6" beyond wall face
3. Set First Course:
- Bury 1/6 to 1/4 of total wall height
- Check level after every block
- Fill cores and voids with gravel
- Use string line for alignment
Base Requirements by Wall Height:
| Wall Height | Buried Depth | Base Thickness | Trench Width |
|---|---|---|---|
| 2 feet | 4-6" | 6" | 30-36" |
| 3 feet | 6-8" | 6" | 36-42" |
| 4 feet | 8-12" | 6-8" | 42-48" |
| 6 feet | 12-18" | 8"+ | Per engineer |
Soil Condition Adjustments:
| Soil Type | Modification Required |
|---|---|
| Clay | Deeper base (8"+), extra drainage |
| Sandy | Standard base, good drainage |
| Rocky | May need concrete leveling pad |
| Organic/peat | Remove entirely, replace with gravel |
| High water table | Engineer required, French drain system |
| Expansive (black gumbo) | Oversized base, flexible joints |
The Cardinal Rule: Never skip the buried course. It provides crucial resistance to sliding and overturning. A wall built on top of the ground WILL fail.
Block and Material Quantity Calculations
Accurate material estimates prevent costly mid-project supply runs and ensure you have matching dye lots:
Block Quantity Formulas:
Standard Calculation:
Blocks = (Wall Length ÷ Block Face Width) × Number of Courses
Courses = Total Height (including buried) ÷ Block Face Height
Quick Reference (blocks per 10 linear feet):
| Block Type | Face Size | Blocks per 10 LF per Course |
|---|---|---|
| Standard SRW | 12"×4" | 10 |
| Large SRW | 16"×6" | 7.5 |
| Small SRW | 8"×4" | 15 |
| Timber 6×6 | 5.5" face | 22 |
| Allan Block AB | 18"×8" | 6.7 |
Example Calculation: Wall: 30 feet long, 3 feet exposed height (+ 6" buried)
- Total height: 3.5 feet = 42"
- Using 12"×4" blocks: 42" ÷ 4" = 10.5 courses (round to 11)
- Blocks per course: 30' × 12" ÷ 12" = 30 blocks
- Total blocks: 30 × 11 = 330 blocks
- Add 10% waste: 330 × 1.10 = 363 blocks
Cap Block Quantities:
- One cap per face foot of wall
- 30 LF wall = 30 caps (plus 5% waste)
- Caps are sold separately, $6-15 each
Drainage Material Quantities:
| Material | Formula | Example (30 LF × 3.5' wall) |
|---|---|---|
| Drain gravel | LF × Height × 1.5' depth × 0.04 | 6.3 cu yd |
| Drain pipe | LF + 10' for outlet | 40 LF |
| Filter fabric | LF × (Height + 3') × 1.1 | 215 sf |
| Geogrid | LF × Grid Length × Layers | 180 sf |
Surcharge and Slope Considerations
Walls near slopes, driveways, or structures face additional loads that require engineering or significant overbuilding:
What is Surcharge? Any load above and behind the wall that adds to soil pressure: vehicles, buildings, slopes, stored materials, even people.
Common Surcharge Scenarios:
| Surcharge Type | Added Load | Engineering Required? |
|---|---|---|
| Level lawn (foot traffic) | Minimal | No |
| Driveway within 4 ft | 250+ psf | Usually yes |
| Parking area | 100-250 psf | Yes |
| Building foundation | 500+ psf | Always yes |
| Pool within 10 ft | 400+ psf | Always yes |
| Slope above wall | Varies | Often yes |
Slope Above Wall - Extra Pressure:
| Slope Angle | Effective Height Increase |
|---|---|
| 1:4 (14°) | Add 25% to wall height |
| 1:3 (18°) | Add 33% to wall height |
| 1:2 (27°) | Add 50% to wall height |
| 1:1 (45°) | Engineer required |
Setback Requirements from Surcharges: To avoid engineering for surcharges, maintain these minimum distances:
| Surcharge | Minimum Setback from Wall Top |
|---|---|
| Driveway | 4 feet + wall height |
| Garage/shed | Wall height × 2 |
| House foundation | Wall height × 3 |
| Swimming pool | 10 feet minimum |
When You MUST Hire an Engineer:
- Wall height exceeds 4 feet
- Surcharge within danger zone
- Poor soil conditions
- Near property lines (liability)
- Multiple tiered walls
- Near water features or streams
DIY vs. Professional Installation
Understanding when to DIY and when to hire professionals can save money and prevent disasters:
DIY-Appropriate Projects:
- Walls under 3 feet tall
- Level ground with good drainage
- No surcharges (driveways, buildings)
- Stable soil conditions
- Decorative/garden walls
- Experienced with landscaping
Hire Professionals For:
- Walls over 4 feet (code requirement)
- Structural walls holding slopes
- Near foundations or driveways
- Poor soil or water problems
- Tight access requiring machinery
- Limited time/physical ability
Cost Comparison (30 LF × 3 ft wall):
| Approach | Materials | Labor | Total |
|---|---|---|---|
| DIY | $900-1,500 | Your time | $900-1,500 |
| Pro Install | $900-1,500 | $1,500-3,000 | $2,400-4,500 |
DIY Time Estimates:
| Task | Time Required |
|---|---|
| Layout and excavation | 4-8 hours |
| Base preparation | 2-4 hours |
| Block installation | 1-2 hours per course |
| Drainage and backfill | 4-6 hours |
| Cap installation | 1-2 hours |
| Total (30 LF × 3 ft) | 16-30 hours |
Tools Needed for DIY:
| Tool | Own/Rent | Cost |
|---|---|---|
| Plate compactor | Rent | $50-80/day |
| String line/stakes | Buy | $15-25 |
| 4' level | Buy/Own | $30-60 |
| Rubber mallet | Buy | $15-25 |
| Hand tamper | Buy | $25-40 |
| Wheelbarrow | Own/Buy | $80-150 |
| Masonry saw | Rent | $60-100/day |
| Safety gear | Buy | $30-50 |
Budget $150-300 for tool rental on a typical DIY project.
Pro Tips
- 💡Spend extra time on the first course—a perfectly level base makes everything else easier. Check level after every single block.
- 💡Compact backfill in 6-8" lifts with a plate compactor. Loose fill settles over time and puts tremendous extra pressure on the wall.
- 💡Slope the finished grade away from the wall top (2% minimum) to prevent water from infiltrating behind the wall.
- 💡Use construction adhesive on cap blocks to prevent displacement from foot traffic, lawn mowers, or freeze-thaw cycles.
- 💡Install drain pipe outlets at the lowest points with a minimum 1% slope—pipes need somewhere to drain or they're useless.
- 💡Order 10% extra blocks from the same dye lot for cutting waste, breakage, and future repairs. Matching colors later is nearly impossible.
- 💡Never use round river rock for backfill—it doesn't lock together and allows soil migration. Use angular crushed stone only.
- 💡For walls over 2 feet, set blocks with slight backward lean (batter) per manufacturer specs. This counteracts the outward force of soil.
- 💡Wrap filter fabric around drain pipe in a "sock" configuration to prevent clogging—the #1 reason drainage systems fail over time.
- 💡Check all local utility locations before digging. Call 811 at least 48 hours before excavation in the US.
- 💡Stage materials along the wall route before starting—constantly walking back for blocks wastes enormous time.
- 💡Plan for temporary erosion control if construction spans multiple days, especially during rainy seasons.
Frequently Asked Questions
The number depends on wall dimensions and block size. For standard 12"×4" face blocks, you need approximately 3 blocks per linear foot per course. A 20-foot wall that is 3 courses tall (12" exposed) needs 60 blocks (20 × 3). For taller walls, add courses and multiply. Always add 10% for cutting, breakage, and future repairs. Our calculator provides exact counts for your specific block and wall dimensions.
