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MaterialCalc — Concrete Strip Footing Calculator

Estimate prepared 09/01/2026. Estimates only; verify against your plans before ordering.

Concrete Strip Footing Calculator

Add up every run. For a rectangle, that is the perimeter.

Usually twice the wall thickness. 16 in under an 8 in wall.

%

Trench walls slump. Fifteen percent is realistic for hand digging.

Result

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A strip footing is a long box of concrete: total run times width times depth. The width is set by the wall it carries and the depth by your frost line, and both are code questions rather than preference. This gives you the volume, the rebar, and what it costs poured against earth.

Assumptions used

These are the numbers behind the result. Where one of them is soft, the cost range widens rather than pretending to a precision the data does not have.

80 lb bag yield
0.6 ft³

Yield of one 80 lb bag of standard concrete mix.

Quikrete product data sheet — Published product data, checked 09/01/2026

Ready-mix short-load threshold
1 yd³

Below roughly one cubic yard, most suppliers add a short-load fee that erases the price advantage over bags.

Regional ready-mix supplier schedules — Rough figure — widens the estimate range, checked 09/01/2026

Bags per pallet
42 bags

Above roughly one pallet of 80 lb bags, ready-mix is usually cheaper and always faster.

Home Depot / Lowe's pallet quantities — Industry standard, varies by supplier, checked 09/01/2026

Concrete cover, earth-cast
3 in

ACI 318 cover requirements — Published product data, checked 09/01/2026

Lap splice length
40 × bar diameter

A common rule of thumb. Engineered work uses the value on the drawings, not this one.

ACI 318 development length, typical case — Rough figure — widens the estimate range, checked 09/01/2026

Prices verified 09/01/2026 (US national average, big-box retail shelf price and regional ready-mix quotes). Regional adjustment: Blended from RSMeans city cost index bands and BLS construction wage differentials.

The formula

Volume = total run length × footing width × footing depth, in consistent units, divided by 46,656 for cubic yards. Rebar assumes two continuous bars with a lap at each splice, so bar footage is run length × 2 plus lap allowance, divided by the 20 ft stick length.

Worked examples

96 ft perimeter, 16x8 footing

Total footing length: 96 Footing width: 16 Footing depth: 8 Waste: 10

About 3.5 cubic yards — a comfortable single ready-mix load for a 24x24 building perimeter.

40 ft of 24x12 footing under a garage wall

Total footing length: 40 Footing width: 24 Footing depth: 12 Waste: 10

Roughly 3.3 yards. A wider, deeper footing on a shorter run uses about the same concrete as a long thin one — width and depth are the multipliers that bite.

20 ft of 16x8 for an addition

Total footing length: 20 Footing width: 16 Footing depth: 8 Waste: 15

Under a yard, so the short-load fee applies and bags are competitive. Note the higher waste allowance — short hand-dug trenches are never neat.

Choosing materials

  • Footing width is normally twice the wall thickness — 16 in under an 8 in wall, 24 in under a 12 in wall. Your local code or engineer sets it against your soil bearing capacity.
  • Depth is measured to the bottom of the footing and has to reach below the frost line. That is 12 in in the South and 48 in or more in the northern tier, and building departments do not negotiate on it.
  • Two continuous #4 bars is the common residential detail, held up on chairs so they sit in the concrete rather than in the dirt. Lap splices are typically 40 bar diameters, about 20 in for a #4.
  • Pouring against earth means the trench is the form. Over-dig one section by two inches over a long run and you have bought yourself an extra half yard of concrete.
  • Keyway or dowels for the wall above have to go in while the concrete is wet. Decide the wall detail before you pour, not after.

Common questions

How wide should a footing be?

The usual rule is twice the wall thickness: 16 in under an 8 in foundation wall, 24 in under a 12 in wall. The real determinant is your soil bearing capacity and the load above, which is why an engineer or your building department has the final say.

How deep do footings need to be?

Below the local frost line, measured to the bottom of the footing. That ranges from 12 in along the Gulf Coast to 48 in or more in Minnesota and Maine. Your building department publishes the number for your jurisdiction.

How much concrete for a 96 ft footing?

At 16 in wide by 8 in deep, 96 linear feet is about 3.2 cubic yards before waste, or 3.5 with a 10% allowance. Width and depth drive this far more than length does.

Do footings need rebar?

Most codes require it, and it is cheap insurance regardless. Two continuous #4 bars is the standard residential detail. The bars must sit up in the concrete on chairs with about 3 inches of cover — bars lying in the trench bottom do nothing.

Can I pour footings and the wall at the same time?

Only in a monolithic pour, which is common in warm climates for slab-on-grade construction. Where footings go below a deep frost line, they are almost always poured first, then the wall is formed on top of them.

How much waste should I allow on trench footings?

Ten percent for machine-dug trenches in stable soil, fifteen for hand digging or loose ground. The trench is the form, so every slumped wall and over-dug section is concrete you pay for.

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