Total linear run of the wall from end to end.Please enter a valid length greater than 0.
Exposed face height. Walls over 4 ft typically require engineering review.Please enter a valid height greater than 0.
Minimum 8 in for walls up to 4 ft high. Walls over 4 ft: 10–12 in minimum.Please enter a valid thickness greater than 0.
Use 10% for standard pours. Add 15% for tapered walls or complex form work.
$
Leave blank to skip cost estimate. US average: $100–$150/yd³ for ready-mix.
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Your Concrete Estimate
Concrete Volume (with waste)
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Cubic Yards (yd³)
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Cubic Feet (ft³)
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Cubic Meters (m³)
Bags Required (includes waste)
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40 lb bags
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60 lb bags
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80 lb bags
—Face Area (ft²)
—Face Area (m²)
—Thickness
—Waste Factor
Estimated Material Cost
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Concrete material cost only. Add forming lumber, rebar, drain gravel, waterproofing, and labor for a full project budget. Use our Full Project Estimator for a complete breakdown.
Step 1: Convert all dimensions to feet
Step 2: Volume (ft³) = Length (ft) × Height (ft) × Thickness (ft)
Step 3: Cubic Yards = ft³ ÷ 27
Step 4: Final Volume = Volume × (1 + waste% ÷ 100)
Step 5: Bags = CEIL(Final ft³ ÷ bag yield) — never round down
Bag yields: 40 lb = 0.30 ft³ | 60 lb = 0.45 ft³ | 80 lb = 0.60 ft³
Face Area (ft²) = Length (ft) × Height (ft)
How to Use This Concrete Retaining Wall Calculator
Measure your wall's three critical dimensions.
Use a tape measure to determine the total linear length of the wall from end to end, the exposed height of the wall face, and the planned wall thickness (stem thickness). If the wall varies in height, calculate each section separately and add the results. Record measurements in whatever unit you find easiest — the calculator converts automatically.
Select units and enter values.
Choose feet, inches, meters, or centimeters from the dropdown next to each field. Length and height most commonly use feet for walls; thickness is often entered in inches. Make sure each field uses its own correct unit — a common mistake is entering thickness in feet when it should be inches.
Set a waste factor.
The default is 10%. Use 15% for walls with curved sections, stepped heights, or if this is your first retaining wall pour. Concrete placed against earthen cuts or rough forms absorbs slightly more material than an equivalent slab — factor this in. Never drop below 5%.
Use your results to order materials and plan your pour.
The cubic yards number is what you quote to the ready-mix supplier. The bag counts apply if you're hand-mixing, though any retaining wall over about 2 cubic yards is far more efficiently poured with ready-mix. If you entered a price per cubic yard, the cost estimate reflects concrete material cost only — add forming lumber, rebar, drain gravel, and waterproofing for your full budget.
⚠ Pro Tip: This calculator computes the concrete volume of the wall stem (the vertical panel). It does not include the footing below grade. A retaining wall almost always requires a concrete footing — typically 12 inches deep and 1.5–2× the wall thickness wide. Use our Footing Calculator alongside this tool for a complete material estimate.
Concrete Retaining Wall Volume Formula
A cast-in-place concrete retaining wall stem is a rectangular prism: length × height × thickness. All three dimensions are converted to feet before multiplying, then divided by 27 to convert cubic feet to cubic yards.
Step
Formula
Example (20 ft × 4 ft × 8 in)
1. Convert thickness to feet
inches ÷ 12
8 ÷ 12 = 0.667 ft
2. Volume in cubic feet
L × H × T
20 × 4 × 0.667 = 53.33 ft³
3. Convert to cubic yards
ft³ ÷ 27
53.33 ÷ 27 = 1.975 yd³
4. Add waste factor (10%)
Volume × 1.10
1.975 × 1.10 = 2.17 yd³
5. Face area for reference
L (ft) × H (ft)
20 × 4 = 80 ft²
Common Retaining Wall Size Reference Table
Concrete volumes for common retaining wall configurations — no waste factor applied. Add 10% for real-world ordering. Footing not included.
Wall Length
Height
Thickness
Cubic Yards
60 lb Bags
80 lb Bags
10 ft
3 ft
8 in
0.74 yd³
56 bags
42 bags
20 ft
3 ft
8 in
1.48 yd³
109 bags
82 bags
20 ft
4 ft
8 in
1.98 yd³
146 bags
110 bags
30 ft
4 ft
8 in
2.96 yd³
219 bags
164 bags
20 ft
4 ft
10 in
2.47 yd³
183 bags
137 bags
40 ft
5 ft
10 in
6.17 yd³
457 bags
343 bags
50 ft
6 ft
12 in
11.11 yd³
822 bags
617 bags
100 ft
4 ft
10 in
12.35 yd³
914 bags
686 bags
Volumes are for the wall stem only. A continuous strip footing adds roughly 0.5–1.5 yd³ per 10 linear feet depending on footing dimensions. Always calculate footing volume separately.
What Thickness Does My Retaining Wall Need?
Wall thickness is the most consequential design decision for a concrete retaining wall. Undersizing the stem is the most common cause of retaining wall failure. The table below reflects minimum practical thicknesses for cast-in-place concrete walls; engineered walls with higher surcharge loads or poor soil conditions will require thicker stems or additional reinforcement.
Recommended minimum concrete retaining wall stem thickness by wall height and application.
Wall Height (exposed)
Min. Stem Thickness
Rebar
Notes
Up to 2 ft
6 inches
Optional
Minimal lateral load; often unreinforced
2–4 ft
8 inches
Recommended
Residential garden walls; #4 @ 12 in o.c. each way
4–6 ft
10 inches
Required
Engineering review recommended; #5 @ 12 in o.c.
6–8 ft
12 inches
Required
Engineering stamp typically required in most jurisdictions
Over 8 ft
Engineered
Required
Always requires licensed structural engineer
Any height — vehicle surcharge
Add 2 in minimum
Required
Parking adjacent to wall increases lateral pressure significantly
Any height — slope above wall
Add 2–4 in
Required
Sloped backfill increases soil pressure; engineer required over 4 ft
The 4-foot rule matters: in most US states, any retaining wall exceeding 4 feet in exposed height from the bottom of the footing requires a building permit and engineered drawings. Check your local codes before forming — pouring without a permit when one is required means the wall may have to come down regardless of quality.
Common Mistakes When Estimating Concrete for a Retaining Wall
⚠️
Forgetting to calculate the footing separately.
This calculator computes stem (wall panel) volume only. Almost every concrete retaining wall requires a continuous strip footing buried below frost depth — often 12–18 inches deep and 18–24 inches wide. Omitting the footing volume means you'll be 30–50% short on a typical wall. Run a separate footing calculation before placing your concrete order.
📐
Measuring to the back of the form instead of the stem face.
If your forms include space for drainage aggregate or a drain pipe channel at the back of the wall, don't include that gap in your wall thickness. Thickness means the thickness of concrete — the stem itself — not the total form depth.
🏗️
Undersizing the wall thickness to save concrete.
The cost difference between an 8-inch and 10-inch wall on a 20-foot run at 4 feet tall is roughly a quarter yard of concrete — about $25–$40. The difference in wall strength and longevity under lateral soil pressure is enormous. Undersized stems are the leading cause of retaining wall failure. Use the thickness guide above and don't undersize.
💧
Not planning for hydrostatic pressure drainage.
Water builds up behind retaining walls and dramatically increases lateral pressure — the leading cause of blowout after poor sizing. Every concrete retaining wall needs weep holes (3-inch diameter every 6–8 feet at the base) or a perforated drain pipe in gravel at the footing. This doesn't affect your concrete volume calculation but must be in your design before the pour.
📅
Pouring without a permit on a wall over 4 feet.
Walls over 4 feet in exposed height require permits and, in most jurisdictions, engineered drawings. Pouring without them puts you at risk of a mandatory teardown regardless of how well the wall is built. Factor permit and engineering costs into your project timeline — they typically take 2–6 weeks.
Frequently Asked Questions
Multiply the wall's length (in feet) by its height (in feet) by its thickness (in feet) to get cubic feet. Divide by 27 to convert to cubic yards. Then multiply by 1.10 to add a 10% waste factor. This calculator gives you all three volumes plus bag counts instantly. Remember: this calculation covers the wall stem only. Your footing — the buried concrete base — must be calculated separately and is typically a significant additional volume. For a 20-foot wall that is 4 feet tall and 8 inches thick, the stem alone requires about 2.2 cubic yards with waste.
No — this calculator computes the volume of the wall stem (the vertical concrete panel) only. A concrete retaining wall almost always requires a separate continuous strip footing buried below frost depth. A typical residential retaining wall footing is 12–18 inches deep and 18–24 inches wide. For a 20-foot wall, that footing alone adds roughly 1.1–2.2 cubic yards of additional concrete. Use our Concrete Footing Calculator to calculate the footing volume separately, then add the two figures together for your total concrete order.
The minimum practical thickness for a cast-in-place concrete retaining wall is 8 inches for walls up to 4 feet tall, with rebar reinforcement. Walls from 4 to 6 feet need at least 10 inches. Walls 6 to 8 feet need at least 12 inches and should be engineered. Any wall over 4 feet in exposed height should have a structural engineer review the design — lateral soil pressure increases with the square of height, so undersized stems fail catastrophically. Surcharge loads (a parking area, slope, or heavy equipment near the top of the wall) require additional thickness beyond these minimums.
In most US jurisdictions, retaining walls exceeding 4 feet in exposed height — measured from the bottom of the footing — require a building permit and, usually, stamped engineering drawings. Some jurisdictions set the threshold at 3 feet. Small decorative landscape walls under 2 feet often don't require permits, but check with your local building department before starting. Building without a permit when one is required can result in mandatory removal of a perfectly sound wall. Permit fees typically run $100–$500 for residential retaining walls; engineering drawings add $500–$2,000 depending on complexity.
Professionally installed cast-in-place concrete retaining walls typically cost $30–$70 per square foot of face area, installed. That range includes forming, rebar, concrete, drainage, waterproofing membrane, and basic backfill. Higher walls, engineered designs, or walls with difficult access push toward the upper end or beyond. Material-only costs — concrete, rebar, forming lumber, drainage gravel, waterproofing — typically run $10–$20 per square foot of face area for a residential wall. Get at least three quotes from licensed contractors; retaining wall pricing varies significantly by region and site access.
Specify a minimum of 3,500 PSI for a residential concrete retaining wall. In freeze-thaw climates, use 4,000 PSI with 5–7% air entrainment to resist surface scaling. If the wall is in contact with soil that may contain sulfates (common in some western US soils), specify a sulfate-resistant cement or a higher-strength mix per your local ready-mix supplier's recommendation. Avoid 3,000 PSI for walls over 3 feet — the modest cost savings are not worth the reduced durability over a 30–50 year service life.
For a wall up to 4 feet tall at 8 inches thick, a minimum of #4 rebar (1/2 inch diameter) at 12 inches on-center in both horizontal and vertical directions is standard practice. Vertical bars must extend down into the footing — typically a 90-degree bend or a length equal to at least 30 bar diameters into the footing. For walls 4–6 feet tall, #5 rebar (5/8 inch) at 12 inches o.c. each way is more appropriate. Any wall requiring an engineering stamp will have a rebar schedule in the drawings — follow it exactly. Our Rebar Calculator can help you estimate the linear footage and weight of steel needed.
Water is the primary cause of retaining wall failure. Hydrostatic pressure from waterlogged backfill can triple the lateral force on a wall. Every concrete retaining wall needs either weep holes — 3-inch diameter PVC pipe sleeves cast through the wall at 6 to 8 feet on center at the base — or a continuous perforated drain pipe in a gravel envelope at the footing, daylighting at each end of the wall. The area directly behind the wall for the first 12–18 inches should be backfilled with clean crushed stone or drain gravel, not compacted clay or silt. Apply a waterproofing membrane to the back of the wall before backfilling in wet climates.
Technically yes, but ready-mix concrete is almost always the right choice for a retaining wall. A 20-foot wall at 4 feet tall and 8 inches thick needs about 2.2 cubic yards of concrete — roughly 200 bags of 60 lb bags. Mixing and placing 200 bags before the earliest pours begin to set is extremely difficult for a single crew, and cold joints (pours against partially set concrete) create structural weak points in a wall that is specifically designed to resist large lateral loads. Reserve bagged concrete for very small walls under 10 feet long and 2 feet tall. Use ready-mix for everything else.
Do not backfill a concrete retaining wall in the first 7 days. Standard practice is to wait a minimum of 7 days before applying any backfill load, and ideally 28 days before placing full design load. Concrete reaches approximately 70% of its 28-day design strength at 7 days and full strength at 28 days. Backfilling too early — even with light gravel — imposes lateral pressure on concrete that hasn't yet developed the strength to resist it, which can cause cracking or outright wall movement. Strip forms no earlier than 24–48 hours after the pour, but keep the wall moist and protected from heat and direct sun while curing.
