How wide should the footing be on a poured concrete retaining wall?

A cantilever concrete retaining wall footing is normally 50 to 70 percent of the total structure height — measured from the bottom of the footing, not from the ground you see. A wall showing 4 ft with its footing 3 ft down is a 7 ft structure, so the footing wants roughly 3.5 to 4.9 ft of width, typically split about one third in front of the stem as the toe and two thirds behind it as the heel. The heel matters most: the soil sitting on it is what holds the wall down. This calculator checks your footing width against that band.

How much concrete does a retaining wall need?

Add the stem and the footing. A 20 ft long wall with a 6 ft tall by 10 in thick stem is 100 cubic feet, and a 4 ft by 12 in footing under it is another 80 — 180 cubic feet, or 6.7 cubic yards neat. With an 8 percent allowance for over-excavation, spillage and form deflection you order about 7.25 cubic yards. The footing is often close to half the concrete, which is why people who price only the visible wall come up short.

Can I use bagged concrete for a retaining wall?

Arithmetically yes, practically almost never. An 80 lb bag yields about 0.6 cubic feet, so the 7.25 cubic yard wall above is roughly 324 bags — several pallets, and a cold joint every time you stop mixing. Bagged mix makes sense below about one cubic yard, or roughly 45 bags. Above that, ready-mix is cheaper per yard and far more likely to give you one monolithic pour, which is what a retaining wall actually needs.

What is a short-load fee on concrete delivery?

Ready-mix suppliers charge a surcharge when you order less than their minimum load, commonly 5 to 8 cubic yards. The fee is typically 50 to 150 dollars flat, though some suppliers instead bill 40 to 80 dollars per undelivered yard. On a small wall this fee can be a fifth of the concrete bill, which is why it is worth checking whether lengthening the pour or combining it with another slab gets you over the minimum. This calculator adds the fee automatically when your order falls short.

Poured Concrete Retaining Wall Calculator

Cubic yards of concrete to order for a cast-in-place retaining wall — stem plus footing, with waste and short-load fees — along with a real rebar schedule including lap splices and footing hooks, form contact area, drain rock and a footing-width check against what a cantilever wall of that height actually needs.

Frost depth (sets footing depth)

Wall length (ft)

Exposed height (ft)

Footing width (ft)

Stem thickness (in)

Footing width is checked against 50–70% of the total structure height — top of wall to bottom of footing, not just the part you can see.

Footing detail, rebar schedule, drainage & prices

Footing — depth comes from the frost preset above

Footing thickness (in)

Footing bottom below grade (in)

Toe projection in front of stem (in)

Whatever is left after the toe and the stem becomes the heel — the part the retained soil sits on and holds down.

Concrete ordering

Waste / over-excavation (%)

Supplier minimum load (cu yd)

Bag yield (cu ft per bag)

0.60 for an 80 lb bag, 0.45 for a 60 lb bag. Only used for the bagged-vs-ready-mix comparison.

Rebar — spacing on centre, both ways

Bar size

Stem verticals spacing (in)

Stem horizontals spacing (in)

Footing transverse spacing (in)

Footing longitudinal bars

Rebar cutting waste (%)

Drainage behind the wall

Drain rock width (in)

Drain rock weight (tons/cu yd)

Filter fabric overlap (%)

Weep hole spacing (ft)

Unit prices — leave any blank to drop it from the total

Concrete / cu yd

Short-load fee

Rebar / lb

Form material / sq ft

Drain rock / ton

Drain pipe / ft

Filter fabric / sq ft

Materials

7.25 cu yd of concrete · about $2,611 in materials

Stem6 ft tall × 10 in thick
Footing4 ft wide × 12 in thick
Toe / heel1.00 / 2.17 ft
Total structure height7 ft
Concrete (neat)6.7 cu yd · order 7.25 in 1 load
Or bagged mix324 bags
Rebar476 ft · 24 sticks · 318 lb
Bar schedule21 verticals @ 7.58 ft · 7 stem rows · 21 footing bars
Form contact area280 sq ft
Drain rock4.4 cu yd · 6.2 tons
Pipe, fabric, weeps30 ft · 154 sq ft · 3 weeps

Concrete (7.25 cu yd)$1,269

Short-load fee$0

Rebar$286

Forms$700

Drain rock$280

Drain pipe$30

Filter fabric$46

Materials total$2,611

Per face sq ft$32.64

Footing width OK Your footing is 4.0 ft wide; a cantilever wall this tall wants 3.5–4.9 ft.

Order ready-mix 7.25 cu yd is about 324 bags of mix — well past the point where a truck is cheaper and gives you one monolithic pour. Your order clears the 5 cu yd minimum, so no short-load fee.

Materials only — no excavation, pump, labour or engineering. Concrete price is a delivered ready-mix rate; see the notes below for where these defaults come from.

A cantilever wall is an L on its side: the stem holds the soil, the heel carries the soil that holds the stem down, and the whole footing sits below frost. Cross-section is schematic, not to scale.

A poured retaining wall over about 4 ft (1.2 m) of exposed height must be engineered. Unlike a dry-stacked wall, a cantilever concrete wall carries its load in the steel, and bar size, spacing and footing geometry come out of a design that checks overturning, sliding and bearing pressure for your soil. This calculator performs none of those checks — the footing-width band here is a planning rule of thumb only. Any wall with a slope, driveway, pool or foundation loading it from above needs a designed wall and almost certainly a permit and inspection, whatever its height. Have utilities located before you dig (811 in the US).

↗ Poured Concrete Retaining Wall Calculator by GRLab — free retaining-wall planning tools

Half the concrete is in the part you never see

A poured retaining wall is priced as if it were the wall, and built as if it were the footing. On the default 20 ft example here the stem takes 100 cubic feet of concrete and the footing takes 80 — and the footing also carries almost all of the rebar complication, because that is where the bars hook and lap. Add the frost requirement, which drives the footing down below the depth your soil freezes to and quietly makes the stem two feet taller than the wall you asked for, and the estimate people make in their head is routinely a third low. This calculator works from the bottom of the footing up.

How each number is worked out

Stem height: exposed height plus the buried part, which is the footing bottom depth minus the footing thickness. With a 36 in frost depth and a 12 in footing, a 4 ft wall has a 6 ft stem and a 7 ft total structure. Every volume below follows the 7, not the 4.
Concrete: stem (length × stem height × thickness) plus footing (length × width × thickness), then a waste allowance for over-excavated footing trench, spillage and form deflection. The result is rounded up to the quarter yard suppliers actually batch in, and compared against their minimum load.
Short-load fee: added automatically when the order falls under the supplier minimum you enter. It is a real line item, not a rounding error — on a small wall it can be a fifth of the concrete bill.
Rebar schedule: stem verticals are counted at your spacing along the wall and each one is measured properly — up the stem less top cover, down through the footing less bottom cover, plus a 90° hook leg into the footing. Stem horizontals are counted up the stem, footing transverse bars across the footing less cover each side, and longitudinal bars run the length. Runs longer than a stock bar get a lap splice of 40 bar diameters added. A cutting-waste allowance then converts linear feet into whole sticks and a weight for pricing.
Form contact area: both faces of the stem plus both edges of the footing. This is the number form suppliers quote against, and it is why a thin tall wall costs more per cubic yard than a thick one.
Footing-width check: a cantilever footing is normally 50–70% of the total structure height, with roughly a third of it in front of the stem as the toe. The tool warns when yours is outside the band, or when the toe and stem alone eat the whole footing and leave no heel — the heel is the part that actually holds the wall down.
Drainage: a column of drain rock behind the stem, a perforated pipe with an outlet run, filter fabric with an overlap, and weep holes at your spacing. A poured wall is impermeable, so unlike a gabion or dry-stacked wall it has no relief unless you build it in.

Where these prices come from

Ready-mix at $175 per cubic yard delivered is the middle of two 2026 US pictures that do not quite agree: Concrete Network's supplier survey put the 2025 national average at $179.95 with a $160–195 range, while consumer cost aggregators for 2026 quote a lower $125–175. We sit inside both. Short-load fees are commonly $50–150 flat below a 5–8 cubic yard minimum, though some suppliers bill $40–80 per undelivered yard instead — enter whatever your supplier quotes. Rebar at $0.90/lb puts #4 bar at about $0.60 per foot, inside the $0.55–0.85 per foot that #4 was listing at in early 2026. Form material at $2.50/sq ft assumes single-use plywood and studs you buy; if you rent reusable panels or already own the lumber, drop it toward zero. Drain rock, pipe and fabric use the same defaults as our other retaining-wall tools so the numbers stay comparable across materials.

This tool estimates a cast-in-place cantilever concrete wall. For segmental concrete block use the full block takeoff; for wood see the timber calculator; for rock-filled baskets the gabion calculator; to compare installed prices across all of them the cost calculator; and for the dig and haul-off under any wall the excavation calculator. Note the per-square-foot figure here is against the exposed face, so it reads higher than the cost calculator's DIY rate — spread over the full structure face the same default wall lands at about $18.65 per square foot, which is where that rate sits. Defaults follow common cantilever practice, not an engineered design — every field is editable.

Poured-wall notes that save money or rework

Pour the footing and stem the same day if you can. If you cannot, a keyway or dowels at the cold joint are not optional — that joint is exactly where the wall wants to slide.
Get over the load minimum. If the order lands at 4.5 yards and the minimum is 5, lengthening the wall or pouring a landing at the same time is often cheaper than paying the short-load fee for concrete you did not receive.
Order by the trench, not the drawing. Footing trenches over-excavate; that is what the waste allowance is for, and a wall that runs short mid-pour is a cold joint you will look at forever.
Brace forms for full liquid head. Fresh concrete pushes about 150 lb per cubic foot sideways. Blown forms on a retaining wall are the single most expensive DIY failure on this list.
Waterproof the back face and drain it. The wall is impermeable, so water that gets behind it stays there. Drain rock, a pipe with somewhere to go, and weeps — all three, not one of them.

Frequently asked questions

How thick should a poured concrete retaining wall be?

Garden-scale cantilever stems are commonly 8–12 in thick, thickening with height and with the bar size the design calls for. Thickness is a structural output, not a preference: it is what gives the vertical bars enough cover and lever arm. The 10 in default here is typical for a wall in the 4 ft range; above that, use the number your engineer gives you.

How deep does the footing have to be?

Below the local frost line, so the ground under it does not heave — commonly 12 in in frost-free regions and 36–48 in across the northern US. Pick the preset that matches your area and the calculator carries the extra depth through the stem height and the concrete volume, which is where it actually costs you.

Is a poured wall cheaper than block?

In materials the two are close; in labour they are not. A poured wall adds forming, bracing and a pour window, which is why installed poured concrete runs about $35–65 per square foot against $30–60 for segmental block. Poured wins on height, on tight radii, and where you want an uninterrupted face. Compare all five materials in the cost calculator.

How much rebar does a retaining wall need?

The default 20 ft example works out to about 476 linear feet — 24 sticks of #4 at 20 ft, roughly 318 lb — from verticals at 12 in, stem horizontals at 12 in, footing transverse bars at 12 in and three longitudinal bars. Spacing and bar size for a real wall come from the engineered design; change them here and the schedule follows.

Do I need drainage behind a poured wall?

More than behind any other type. Block and gabion walls leak by nature; a poured wall does not, so hydrostatic pressure builds against the full face. Drain rock, a perforated pipe that daylights, filter fabric and weep holes are the standard package — size the rock and pipe in the drainage calculator.

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