Poured foundation, retaining, or garden wall. Get volume, rebar, formwork, drainage, and bags-vs-truck cost.
Optional: openings, waste, pricing
Openings (windows, doors, vents)
Waste and pricing
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How this calculator works
A concrete wall is a volume problem with three complications that most calculators ignore: openings (windows and doors that deduct from the total), retaining-wall taper (the wall gets thicker at the bottom because soil pressure increases with depth), and formwork (which is often 25–40% of the wall cost, not a rounding error).1
Volume = Length × Height × Average thickness − Openings
Retaining taper: Avg thickness = (Top + Bottom) ÷ 2
Formwork area = 2 × Length × Height (both faces)
Rebar = Vertical bars + Horizontal bars + Dowels + 10% lap
The formwork line is the hidden cost. A 40 ft × 8 ft wall needs 320 linear feet of form per face — or 640 LF total if you count both sides. At $4–$6 per LF per use, that is $2,560–$3,840 in formwork alone, which often exceeds the concrete cost. The calculator shows it as a separate line because most DIY estimators forget it entirely.
When a wall needs an engineer
This is where the calculator earns its keep. Most jurisdictions allow small garden walls to be built without engineered design, but structural walls cross a line quickly. The thresholds below are typical — your local code will control.
| Wall type | Height threshold | What triggers engineering | Typical cost |
|---|---|---|---|
| Garden / privacy wall | ≤ 4 ft above grade | Usually none — DIY or contractor | — |
| Garden / privacy wall | 4–6 ft | Permit + review in most jurisdictions2 | $150–$400 permit |
| Garden / privacy wall | > 6 ft | Engineer stamp required in most jurisdictions | $400–$800 plan review |
| Retaining wall | ≤ 3 ft | Usually exempt if no surcharge above | — |
| Retaining wall | 3–4 ft | Permit + review; engineer if slope above | $200–$500 |
| Retaining wall | > 4 ft | Engineer stamp + drainage plan required3 | $500–$2,000 |
| Foundation / basement wall | ≤ 8 ft | Permit + stamped drawings | $500–$1,500 |
| Foundation / basement wall | > 8 ft | Engineer + soil report | $1,000–$3,500 |
Retaining wall taper — why the bottom is always thicker
Soil pressure on a retaining wall increases with depth. At grade, the wall resists almost nothing; at the bottom of a 4 ft wall, it resists about 30 psf of active soil pressure on a typical drained wall, or 100 psf if the soil is saturated. The wall has to be thicker at the bottom to resist that moment.3
| Wall height | Typical top thickness | Typical bottom thickness | Approximate taper |
|---|---|---|---|
| 2 ft | 6″ | 8″ | +1″ per foot |
| 3 ft | 6″ | 9″ | +1″ per foot |
| 4 ft | 8″ | 12″ | +1″ per foot |
| 6 ft | 8″ | 16″ | +1.33″ per foot |
| 8 ft | 10″ | 20″ | +1.25″ per foot |
Field note from the estimating desk: the two mistakes that cost the most on concrete walls are (1) treating a retaining wall as a constant-thickness slab, which under-orders concrete by 20–40% on the tapered section, and (2) skipping the drainage system. A retaining wall without weep holes and gravel backfill will fill with water, and the soil pressure after a heavy rain can be 2–3 times the design load — enough to crack the wall or push it over. The drainage line on this calculator is not optional; if the calculator flags it and you skip it, you are gambling against water pressure, and water pressure wins. Second mistake: not installing form-release oil. A wall form that is bonded to the concrete on both sides has to be broken off, which chips the wall face and can split a 40 ft wall at its weakest point.
Frequently asked questions
How much concrete do I need for a wall?
Volume = length × height × thickness, minus openings. A 40 ft × 8 ft × 8″ foundation wall is 21.3 cubic feet or 0.79 cubic yards. For a tapered retaining wall, use the average thickness: a 4 ft wall with 8″ top and 12″ bottom has a 10″ average. Always add 5–10% waste for overpour and uneven formwork.
Do I need a permit for a concrete wall?
Yes in almost every US jurisdiction, at any height above 30–36 inches.2 Garden walls under 4 ft may be exempt in rural jurisdictions, but most cities require a permit for any wall over 3 ft above grade. Retaining walls over 4 ft almost always require engineered drawings plus a drainage plan. Check with your local building department before forming.
How thick should a retaining wall be?
Rule of thumb: the wall should be at least 1/3 its height at the base for a gravity wall, or 6–8 inches minimum for a reinforced concrete wall. A 4 ft wall is typically 8″ at the top and 12″ at the bottom. A 6 ft wall is 8″ at the top and 16″ at the bottom. Anything below these minimums needs engineered design.
How much rebar does a concrete wall need?
Standard residential walls use #4 rebar at 12–18 inches on center in both directions, placed at the mid-plane of the wall with 1.5 inches of clear cover to each face.4 Plus dowels at 12–24 inches on center connecting the wall to its footing. Retaining walls often use larger bars (#5) or tighter spacing (#5 @ 12″ OC) depending on the soil pressure and height.
How much does formwork cost for a concrete wall?
Formwork is often 25–40% of the wall cost. Rental aluminum forms run $6–$8 per linear foot per use; wood forms run $4–$6 per LF for a one-time use; owned reusable forms cost about $1–$2 per LF per use amortized. For a 40 ft × 8 ft wall, that is $480–$640 for one face, or $960–$1,280 for both faces. The calculator includes this as a separate line so you can see the real total.
How much does a retaining wall cost per square foot?
A poured concrete retaining wall runs $20–$40 per square foot of wall face in 2026, including concrete, rebar, formwork, and drainage. A 4 ft × 40 ft wall (160 sq ft of face) runs $3,200–$6,400. Add $200–$2,000 for engineering if the wall exceeds 4 ft. Block retaining walls run $15–$30 per sq ft of face; timber walls run $10–$20 per sq ft.
Bags or ready-mix for a concrete wall?
Always ready-mix for anything larger than a 4 ft × 4 ft wall. A 40 ft × 8 ft wall is 0.79 cubic yards — technically in bags territory — but bags mean 105+ sixty-pound mixes poured in 6 foot lifts, which is physically impossible to do without cold joints. Ready-mix delivers in 15 minutes. Even a small wall benefits from a short-load truck, because the quality of the pour is far higher.
How long does a concrete wall take to build?
Formwork is the slow part: 1–2 days for a 40 ft wall including rebar placement and form bracing. Pour takes 2–3 hours. Stripping forms runs 24–72 hours. Backfill (for foundation walls) or drainage gravel (for retaining walls) can begin after 7 days. Full strength is 28 days.5 Total timeline including cure: 2–4 weeks.
What is the minimum thickness of a foundation wall?
8 inches for a poured concrete foundation wall supporting a single-story residential structure on average soil.2 Thicker (10″ or 12″) for two-story structures, steep backfill, or poor soil. Below 8 inches, you need engineered design even for a single-story house. Basement walls (which resist backfill pressure) are typically thicker than foundation walls for the same reason.
Can I pour a concrete wall without a footing?
No for any structural wall. A footing spreads the wall load across the soil. A wall directly on grade will settle unevenly and crack along its length. For garden walls, a 6–8 inch thick × 12 inch wide footing is sufficient; for foundation walls, the footing must be engineered to local soil conditions. Dowels connecting the wall to the footing are what actually hold the wall in place — without them, the wall can slide off the footing under lateral load.
Standards and sources
- Portland Cement Association — Concrete Walls: Design and Construction. Formwork requirements, volume calculations for tapered walls, and construction sequence. cement.org
- International Code Council — IRC R404 Foundation Walls and R606 Masonry. Height thresholds, permit requirements, and minimum thicknesses. codes.iccsafe.org
- International Code Council — IRC R404.4 Retaining Walls and IBC 1807. Soil pressure design requirements and drainage plan thresholds. codes.iccsafe.org
- Concrete Reinforcing Steel Institute — Reinforcement for Walls. Minimum rebar, spacing, clear cover, and dowel requirements. crsi.org
- American Concrete Institute — ACI 347 Guide to Formwork for Concrete and ACI 308 Curing. Formwork timing, form removal, and curing requirements. concrete.org
- American Concrete Institute — ACI 318 Building Code Requirements. Structural wall design, minimum reinforcement, and cover requirements. concrete.org
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Estimates only. Confirm wall thickness, rebar, drainage, and engineering requirements with a structural engineer or your local building department before forming and pouring. Last reviewed October 2026.