Concrete Footing Calculator: Bags per Linear Foot

A footing is a long, shallow trench of concrete, so the count that matters is per linear foot. The standard residential strip footing is 16 inches wide × 8 inches deep. Here is what it takes.

Footing Bag Table: Bags per 10 Linear Feet, by Footing Size

Exact counts are the mathematical minimum, rounded up. The "with waste" counts multiply the volume by 1.10 before dividing, which is the number to actually buy. Yields: 80 lb bag = 0.60 ft³, 60 lb = 0.45 ft³, 40 lb = 0.30 ft³.

To scale the table: find your footing size, take the per-10-ft count, and multiply by your total trench length divided by 10. A 60 ft run of 16 in × 8 in footing at the with-waste count is 17 × 6 = 102 bags of 80 lb mix. Odd trench lengths are exactly what the main calculator is for — enter the trench as a slab with the footing's width as one side and the total length as the other.

How Footing Sizes Are Chosen

A footing spreads the load of the wall above it over enough soil that the structure does not settle. Two dimensions do the work, and both are set by your situation, not by preference:

1. Width depends on the load and the bearing capacity of your soil. Wider footings spread the same load over more ground. The 16 in × 8 in size in the quick answer is the common starting point for a one-story wall on average soil.
2. Depth has two parts: the thickness of the concrete itself, and how far down the trench goes. The bottom of the footing must sit below the local frost line, so the trench depth in cold climates is mostly about frost, not strength.
3. Local code sets the minimums. Frost depth, minimum width, and reinforcement requirements vary by jurisdiction and by what the footing carries. The sizes in the table are common examples for estimating concrete — confirm your required size with your local building department or a licensed professional before you dig.

Volume (ft³) = (W ÷ 12) × (D ÷ 12) × length in feet  ·  Bags = ft³ ÷ yield, rounded up

Worked example: a 16 in × 8 in footing runs (16 ÷ 12) × (8 ÷ 12) = 0.89 ft³ per linear foot. Over 10 ft that is 8.89 ft³, and 8.89 ÷ 0.60 = 14.8, so 15 bags of 80 lb mix exact — or 17 with the 10% cushion.

Worked Example: Footings for a 20 × 30 ft Building

A 20 × 30 ft building has a 100 ft perimeter, so it needs 100 linear feet of footing. At 16 in × 8 in, that is 100 × 0.89 = 88.9 ft³, or 3.29 yd³ of concrete: 149 × 80 lb bags exact, 163 bags to buy with waste.

That volume is well past the 1 yd³ crossover where a ready-mix truck usually beats bags — ready-mix suppliers bill a 1 yd³ minimum, which only makes bags cheaper on pours under a yard. At the example prices used on the main calculator ($6.50 per 80 lb bag, $160 per cubic yard, $75 delivery):

Labor settles it further. 163 bags at 80 lb is 13,040 lb of material to lift and mix, and a footing trench needs the whole run placed while the concrete is workable. A truck places the same footing in a single pass. Bags still make sense for short footing runs — a few fence or deck footings, a small shed, a repair — or where a truck simply cannot reach the trench. Run your own quotes through the cost comparison on the calculator before deciding.

Different Footing Size or Length?

Enter the trench in the free calculator as a rectangle: the footing width as one side, the total trench length as the other, and the footing depth as the thickness. It figures cubic yards, cubic feet, and bag counts live, and compares bag cost against a ready-mix quote with your local prices. Pouring a slab instead? See the bags per cubic yard guide or the 10×10 slab bag guide.

Open the Concrete Calculator →

Footing Concrete FAQ