How Much Concrete for a Retaining Wall Footing?

How much concrete for a retaining wall footing depends on the footing’s width, depth, and length. A 16-inch-wide by 8-inch-deep footing, a common size under an 8-inch block wall, takes about 0.89 cubic feet per foot, or about 0.33 cubic yards for every 10 feet of wall. A larger 24 by 12 inch footing takes 2 cubic feet per foot, or about 0.74 cubic yards per 10 feet. Taller walls need engineered footings, so the numbers below are for estimating, not design.

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Concrete per 10 feet of footing

Footing (width x depth)	Cu ft per foot	Cu yd per 10 ft	Cu yd per 50 ft
12 x 8 in	0.67	0.25	1.23
16 x 8 in	0.89	0.33	1.65
20 x 10 in	1.39	0.51	2.57
24 x 12 in	2.00	0.74	3.70
36 x 12 in	3.00	1.11	5.56

Formula: width (ft) × depth (ft) × length (ft) ÷ 27 = cubic yards. Add 5 to 10 percent for trench walls that are wider than planned. Trenches dug by machine almost always come out wider than the bucket.

Which walls use a concrete footing?

Poured concrete walls and mortared block walls sit on a continuous concrete footing, usually with rebar.
Segmental retaining walls (dry-stacked interlocking blocks) usually sit on a compacted gravel leveling pad, not concrete. See retaining wall base gravel.
Stone or brick garden walls under about 2 feet may use either, depending on local practice.

Rough sizing rules

For a mortared block wall, a common starting point is a footing twice the wall thickness in width and about as deep as the wall is thick. So an 8-inch block wall gets a 16 by 8 inch footing, and a 12-inch wall gets a 24 by 12 inch footing. The footing should sit below the frost line in cold climates. Retaining walls hold back soil and water pressure, and many codes require an engineer for walls over about 4 feet tall, or shorter walls with a slope or a driveway above them.

Example: 40-foot block wall

A 40-foot mortared block wall on a 16 by 8 inch footing needs 40 × 1.333 × 0.667 = 35.6 cubic feet, or 1.32 cubic yards. Add 10 percent and order about 1.5 yards. In bags, that would be about 60 bags of 80-pound concrete, so a small ready-mix load is usually easier.

Rebar and keys

Footings for retaining walls usually get two or more horizontal bars, plus vertical dowels that tie into the wall cores. Some designs add a key, a downward lip under the footing that resists sliding. A key adds volume: a 12 by 12 inch key adds 1 cubic foot per foot of wall.

Drainage counts more than concrete

Most retaining wall failures come from water pressure, not a thin footing. Plan for free-draining gravel behind the wall, a perforated drain pipe at the base, and weep holes or outlets. That gravel is a separate order; see our post on retaining wall base gravel.

Bottom line

Estimate retaining wall footing concrete by multiplying width, depth, and length in feet and dividing by 27. A 16 by 8 inch footing takes about a third of a yard per 10 feet, and a 24 by 12 inch footing takes about three quarters of a yard. Segmental walls usually use a gravel pad instead, and tall walls need an engineer’s design.

Questions people ask

How much concrete do I need for a 50-foot retaining wall footing?

About 1.65 cubic yards for a 16 by 8 inch footing or 3.7 cubic yards for a 24 by 12 inch footing, before waste.

How wide should a retaining wall footing be?

A common starting point is twice the wall thickness, but taller or loaded walls need an engineered design.

Do segmental retaining walls need a concrete footing?

Usually not. Most sit on a compacted gravel leveling pad per the block manufacturer’s instructions.

How deep should a retaining wall footing be?

Deep enough to meet the design and, in cold climates, below the frost line.

Does a retaining wall footing need rebar?

Mortared and poured walls typically use rebar in the footing and dowels into the wall.

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