How Much Concrete for Square Column Pads?
Concrete to buy
2.93 cubic yards
Four square 24 in pads, 4 ft below grade with 6 in standing above, ten percent waste.
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How that number is worked out
These are the figures this page was built with and every line the calculator produces from them. Change anything above and all of it moves.
- Pier shapeSquare pad or form
- Diameter or side24 in
- Depth below grade4 ft
- Height above grade6 in
- How many piers4 count
- Waste allowance10 %
Concrete to buy2.93 cubic yards
| Height of each pier | 4.5 ftbelow grade plus what stands above it |
|---|---|
| Section area | 4 sq ftsquare |
| Concrete per pier | 18 cu ft |
| Concrete for all piers | 72 cu ft |
| With waste | 79.2 cu ft |
| 60 lb bags | 1760.45 cu ft each |
| 80 lb bags | 1320.60 cu ft each |
| Form board | 32 ftfour sides of each form |
| Vertical rebar | 68 ft4 bars per pier |
| Bearing at 2,000 psf | 8,000 lbper pier, presumptive soil |
The material list this produces
| Concrete, cu yd | 3 |
|---|---|
| Or 80 lb bags | 132 |
| Form board, ft | 32 |
| Rebar, ft | 68 |
| Rebar tie wire, lb | 1 |
| Post bases or anchor bolts | 4 |
Pad size compared
Pad size swept with the depth and the count held. The two columns are the section area and what each pad carries on presumptive 2,000 psf soil, and they are the same number twice, because bearing is just the area multiplied by the soil. It is worth seeing them side by side, since the area is what doubles and the concrete follows it.
| Pad size | Concrete to buy | Section area | Bearing at 2,000 psf |
|---|---|---|---|
| 12 in square | 0.73 cubic yards | 1 sq ft | 2,000 lb |
| 16 in square | 1.3 cubic yards | 1.778 sq ft | 3,556 lb |
| 18 in square | 1.65 cubic yards | 2.25 sq ft | 4,500 lb |
| 24 in square | 2.93 cubic yards | 4 sq ft | 8,000 lb |
| 30 in square | 4.58 cubic yards | 6.25 sq ft | 12,500 lb |
| 36 in square | 6.6 cubic yards | 9 sq ft | 18,000 lb |
What else matters here
Four 24 in square pads, 4 ft below grade with 6 in above, come to 18 cu ft each and 2.93 cu yd in total. That is 132 eighty pound bags and 32 ft of form board, and at 8,000 lb of bearing each these are carrying something real: a garage column, a porch post taking a roof load, a beam pocket.
The first thing to know about a square pad is that it beats a round pier at the same stated size, and by more than it looks. A 12 in square is 1 sq ft of bearing. A 12 in round is 0.785. The hole is the same width, the form costs about the same, and the square carries 2,000 lb against 1,571. That is 27 percent more bearing for nothing except a different form.
The second thing is that at 2.93 cu yd this stopped being a bag job some way back. One hundred and thirty two bags is over ten thousand pounds of material, and it also has to go in fast enough that the pads are monolithic rather than four separate cold joints. That is a truck, and the 32 ft of form board is the real shopping list item here along with the 68 ft of rebar.
The table below is the size decision. Going from 18 in to 24 in takes the bearing from 4,500 lb to 8,000 for the same depth, and going to 30 in takes it to 12,500. The area is the squared term, so every step up buys a lot. What size the load actually needs is the engineer's call, and on anything carrying a roof or a beam it should be.
What this calculator assumes
- Depth below grade is measured to the bottom of the pier. A footing that stops above the frost line heaves, and the frost depth where you are building is published by your building department.
- Concrete yields are the printed ones: a 60 lb bag makes 0.45 cubic feet and an 80 lb bag makes 0.60.
- Sonotube is nested out of 12 ft lengths rather than divided into them, so a 4.5 ft pier gets two out of a tube and a 6.5 ft pier gets one. The tube line is what you actually buy.
- Bearing is shown at 2,000 pounds per square foot, which is the presumptive value most residential codes allow without a soils report. Soft or filled ground is less and a report can allow more.
- Vertical steel is two bars in a pier under 10 inches, three from 10 to 16, and four above that, each run the full height with three inches of cover at the bottom.
- Anything over about a cubic yard in total is usually cheaper and far faster from a ready mix truck with a short load fee than it is from bags.
Questions people ask
How much concrete for a 24 in square footing pad?
A 24 in square pad 4 ft below grade with 6 in above is 18 cu ft, about 30 eighty pound bags. Four of them is 2.93 cu yd and 132 bags, which is a ready mix job rather than a bag job.
Is a square pad better than a round pier?
At the same stated size, yes, by 27 percent. A 12 in square is 1 sq ft of bearing and a 12 in round is 0.785, so the square carries 2,000 lb against 1,571 for the same width of hole.
How much form board does a square pad need?
Eight feet per pad at 24 in square, which is the four sides. Four pads is 32 ft, and unlike a sonotube the boards can usually be stripped and reused.
The concrete footing calculator takes any dimensions you like and hands back the same list.