How thick should a concrete wall be?

Residential basement walls are typically 8–10 inches thick. Retaining walls range from 8 to 24 inches depending on height and load. Foundation walls are usually 8–12 inches for residential construction.

How do I calculate concrete for a wall?

Use the formula: Volume (yd³) = Length × Height × Thickness (all in feet) ÷ 27. For an 8-inch wall, thickness = 0.667 ft. A 30 ft × 8 ft wall at 8 inches: (30 × 8 × 0.667) ÷ 27 = 5.93 yd³.

What PSI concrete should I use for a poured wall?

Basement and foundation walls typically require 3,000–4,000 PSI concrete. In areas with freezing temperatures or wet soils, specify 4,000 PSI with a low water-to-cement ratio (0.40–0.45) for improved watertightness and freeze-thaw durability. Retaining walls may require 3,500–4,500 PSI depending on load and soil pressure.

When should I use a poured concrete wall vs. a concrete block wall?

Poured concrete walls are stronger, more watertight, and faster to build when you have access to a ready-mix truck. Concrete block (CMU) walls are easier for DIYers since no forms or heavy equipment are needed. For basement foundations over 8 feet tall or any wall with high lateral pressure, poured concrete is generally preferred by structural engineers.

How much rebar does a concrete wall need?

A standard residential basement wall requires vertical #5 rebar every 18–24 inches and horizontal #4 rebar every 24–48 inches, per ACI 318 minimum steel requirements. Retaining walls and walls over 10 feet tall typically need engineered rebar layouts. Always consult local building codes — many jurisdictions require permitted drawings for poured foundation walls.

How do you waterproof a poured concrete wall?

Waterproofing is critical for below-grade concrete walls. The most reliable method is a full waterproofing membrane applied to the exterior (soil side) of the wall before backfilling — crystalline, sheet-applied, or spray-applied products are all effective. Interior drain tile at the footing level, connected to a sump pit, handles any water that gets past the membrane. Applying a waterproofing admixture to the concrete mix (e.g., Xypex or Kryton) reduces permeability from the inside. Interior coatings alone are not adequate for wet conditions — they can delaminate under hydrostatic pressure.

How long does a poured concrete wall take to cure before backfilling?

Wait at least 7 days before backfilling against a poured concrete wall — at that point the concrete has reached approximately 70% of its 28-day design strength. Backfilling too early can impose lateral soil pressure on a wall that has not yet developed adequate strength, causing cracking or structural failure. For walls taller than 8 feet or in wet conditions, wait the full 28 days or consult a structural engineer before backfilling.

Concrete Wall Calculator — Volume for Poured Walls

Estimates volume and bags for poured concrete walls, retaining walls, and basement walls.

What Is a Poured Concrete Wall?

Use this concrete wall calculator to estimate material for a poured (cast-in-place) wall — formed by erecting temporary forms, typically steel, aluminum, or plywood, and filling the space between them with ready-mix concrete. Once the concrete cures and the forms are stripped, the result is a monolithic wall with greater structural integrity and watertightness than a block wall. Poured walls are standard for basement foundations, retaining walls, and any wall that must resist significant lateral pressure from soil or water.

Standard residential poured concrete walls are 8–10 inches thick for basements and foundations, and 8–24 inches thick for retaining walls depending on height and soil pressure. ACI 318 requires a minimum of 3,000 PSI concrete and vertical plus horizontal rebar for most structural wall applications. For basement walls in contact with soil or water, a water-to-cement ratio of 0.45 or less and a waterproofing membrane on the exterior are required by IRC R406 to prevent moisture infiltration.

How to Use This Concrete Wall Calculator

This concrete wall calculator estimates the volume for poured concrete walls — basement walls, retaining walls, stem walls, and foundation walls. Enter the wall length, height, and thickness to get the volume in cubic yards, cubic feet, and the number of bags needed. For estimating block walls, visit our concrete block calculator.

Concrete Wall Volume Formula

Volume (yd³) = Length (ft) × Height (ft) × Thickness (ft) ÷ 27

Convert thickness from inches to feet by dividing by 12: an 8-inch wall = 0.667 ft, a 10-inch wall = 0.833 ft, a 12-inch wall = 1.0 ft.

Example: Basement Foundation Wall

A basement wall that is 30 feet long, 8 feet tall, and 10 inches thick: Volume = 30 × 8 × 0.833 ÷ 27 = 7.40 cubic yards. With 10% waste, order 8.1 cubic yards.

Example: Retaining Wall

A retaining wall 20 feet long, 4 feet tall, and 12 inches thick: Volume = 20 × 4 × 1.0 ÷ 27 = 2.96 cubic yards.

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Concrete Specifications for Walls

The right concrete mix for a wall depends on its structural role and exposure conditions:

Basement and foundation walls — use 3,000–4,000 PSI concrete with a low water-to-cement ratio for durability and watertightness
Retaining walls — 3,500–4,500 PSI with proper drainage design; consider waterproofing membrane on the soil side
Exposed decorative walls — 4,000 PSI with air entrainment (5–7%) for freeze-thaw resistance
Rebar requirements — most structural walls require vertical and horizontal rebar on specified spacing; consult local codes or a structural engineer

How Much Does a Concrete Wall Cost?

The cost of a poured concrete wall depends on three main factors: the volume of concrete, labor, and formwork. In 2025–2026, ready-mix concrete runs $130–$170 per cubic yard delivered. For a typical 30-foot basement wall (8 ft tall, 10 in thick, ~7.4 yd³), the concrete alone costs roughly $960–$1,260.

Labor and formwork add significantly to the total. Professional wall forming and pouring typically runs $8–$16 per square foot of wall face. That same 30 × 8 ft wall (240 sq ft) would cost $1,920–$3,840 for labor, bringing the all-in price to roughly $2,900–$5,100. Shorter retaining walls are cheaper per linear foot — a 20 ft × 4 ft retaining wall (~3 yd³) typically totals $1,500–$3,000 including excavation and backfill.

To get an accurate material cost for your specific wall, use this calculator to find the volume, then multiply by your local per-yard price. For a full project cost breakdown, try our concrete cost calculator.

Tips for Forming and Pouring Concrete Walls

Brace forms adequately — wet concrete exerts enormous lateral pressure; under-braced forms can blow out, wasting both time and material
Pour in lifts — for walls taller than 4 feet, pour concrete in 2-foot lifts and consolidate each lift before adding the next
Vibrate thoroughly — use an internal concrete vibrator to eliminate air pockets and honeycombing, especially around rebar
Cure before stripping — leave forms in place for at least 12–24 hours (24–48 hours in cool weather) before removing
Wet cure for 7 days — keep the wall surface moist with burlap and plastic sheeting to achieve full design strength
Calculate the full foundation — if your wall sits on a continuous footing, use our concrete calculator to estimate both the wall and footing volumes and order them together

Sources & References

ACI 318-19: Building Code Requirements for Structural Concrete — American Concrete Institute
ASTM C94/C94M: Standard Specification for Ready-Mixed Concrete — ASTM International
PCA: Design and Control of Concrete Mixtures (16th Edition) — Portland Cement Association

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Concrete Wall Calculator