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Strip / pad footings / bags

Concrete Footing Calculator

A 40 ft strip footing 16 in wide and 12 in deep with 4 square pads 24 in across and 12 in deep holds 69.33 cu ft (2.57 cu yd): 155 bags of 60 lb.

Sources checked

Your numbers

Under a wall: the run of the footing. Enter 0 for pads only.

Square footings under posts or columns. Enter 0 for a strip only.

Spill and uneven trench. The form adds none.

Your estimate

155 bags of 60 lb

69.33 cu ft (2.57 cu yd) of concrete in the footing.

FootingLive sketch
strip 40 ft, 16 in wide, 12 in deep; 4 pads, 24 in square
  • Strip
    53.33 cu ft
  • Pads
    16 cu ft
  • 80 lb bags115.56 before rounding
    116 bags
  • 50 lb bags184.89 before rounding
    185 bags
  • 40 lb bags231.11 before rounding
    232 bags

Concrete for a strip footing and pads

  1. The strip is a long block: run x width x depth. For 40 ft, 16 in wide and 12 in deep: 40 x 16 / 12 x 12 / 12 = 53.33 cu ft.
  2. Each square pad is side x side x depth, in feet. 4 pads 24 in square and 12 in deep make 4 x 2² x 1 = 16 cu ft.
  3. Add them: 69.33 cu ft, which is 2.57 cu yd. Divide by what one bag makes, 0.45 cu ft for 60 lb, and round up: 69.33 / 0.45 = 154.07, so 155 bags. For each bag's yield see how many cubic feet in a bag of concrete.

Numbers we use

One 60 lb bag makes
0.45 cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
One 80 lb bag makes
0.6 cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)

A 40 ft strip by width and depth

Cubic yards of concrete in a 40 ft strip footing, by its width (rows) and depth (columns). Sizes to compare, not a code minimum: the depth your code or engineer sets is the one to use.
Width8 in deep12 in deep18 in deep
12 in0.99 cu yd1.48 cu yd2.22 cu yd
16 in1.32 cu yd1.98 cu yd2.96 cu yd
18 in1.48 cu yd2.22 cu yd3.33 cu yd
24 in1.98 cu yd2.96 cu yd4.44 cu yd

Footing questions

How much concrete goes in a 40 foot footing?

The strip alone, 40 ft by 16 in wide and 12 in deep, is 53.33 cu ft, or 1.98 cu yd: 119 bags of 60 lb or 89 of 80 lb.

How many bags for a 24 inch square pad?

A pad 24 in square and 12 in deep holds 4 cu ft: 9 bags of 60 lb or 7 of 80 lb. Each extra pad adds the same.

How deep should a footing be?

This calculator uses the depth you enter and sets none. The frost depth for a place is on the post depth page; your local code or an engineer sets the rule for your footing.

What is the difference between a strip footing and a pad?

A strip, or continuous, footing runs under a wall as one long ribbon. A pad is a square block under one post or column. The form counts both and adds them together.

What about round piers?

A round pier or a column in a form tube is a cylinder, counted by its diameter and length on the Sonotube concrete calculator.

Do footings need rebar?

Steel in a footing is set by your engineer or local code, not by this page. The rebar calculator counts bars for a slab grid, which is a different job.

Should I add extra concrete to a footing order?

The form adds none by default. Enter a percentage in Extra to cover spill and an uneven trench; each bag size then rises by that share, and the page rounds up.

A planning aid, not an engineering calculation: your local code and building inspector have the final word. Terms