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How Much Concrete for 24 Feet of Footing?

For 24 linear feet of a 16 by 8 inch footing, plan on about 0.79 cubic yards. How much concrete for 24 feet of footing at other sizes is in the table; trench footings poured against the soil often use more than the math because trench walls are never perfectly straight.

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Footing math

  1. Cross-section: 16 in × 8 in = 1.333 ft × 0.667 ft = 0.889 sq ft.
  2. Volume: 0.889 × 24 ft = 21.3 cu ft.
  3. Yards: ÷ 27 = 0.79 yd³.

Yards for common footing sizes over 24 feet

Footing (width × depth)Cubic feetCubic yardsYards +10%
12 × 6 in12.00.440.49
16 × 8 in21.30.790.87
20 × 8 in26.70.991.09
24 × 10 in40.01.481.63
24 × 12 in48.01.781.96

How big the footing should be

Code and soil bearing decide the footing size. Light walls often sit on 12 to 16 inch wide footings, while two-story loads or weak soils call for wider ones. Whatever the size, the bottom has to reach undisturbed soil below frost depth. See footing depth and the frost line.

Trench pours run over

Earth-formed trenches eat extra concrete. Over-digging by an inch on each side of a 16-inch footing adds about 12 percent. Measure the trench after digging and size the order from those numbers.

Rebar and inspection

Footing steel is usually two or more horizontal bars held up off the soil. Book the inspection first, then the concrete: a failed inspection with a truck on the way is an expensive afternoon.

Questions people ask

How many yards for 24 feet of 16x8 footing?

About 0.79 cubic yards before waste.

How many yards for 24 feet of 24x12 footing?

About 1.78 cubic yards.

How much extra should I order for a trench footing?

About 10 to 15 percent, since trench walls are rarely straight.

How deep should a footing be?

Below the local frost line and on undisturbed soil; your building department sets the minimum.

When is bagged concrete practical?

Usually for jobs under about a cubic yard. Beyond that, mixing dozens of bags by hand gets slow and batches may not blend well.

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