How Much Concrete for Deck Footings?
Concrete to buy
1.3 cubic yards
Nine round 12 in piers, 4 ft below grade with 6 in standing above, ten percent waste.
When the figures look right, the footing material list downloads as a real PDF with your business details on it, built inside your own browser. Nothing you type is uploaded anywhere.
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 shapeRound, sonotube
- Diameter or side12 in
- Depth below grade4 ft
- Height above grade6 in
- How many piers9 count
- Waste allowance10 %
Concrete to buy1.3 cubic yards
| Height of each pier | 4.5 ftbelow grade plus what stands above it |
|---|---|
| Section area | 0.785 sq ftround |
| Concrete per pier | 3.53 cu ft |
| Concrete for all piers | 31.8 cu ft |
| With waste | 35 cu ft |
| 60 lb bags | 780.45 cu ft each |
| 80 lb bags | 590.60 cu ft each |
| Sonotube at 12 ft | 52 piers cut from one tube |
| Vertical rebar | 115 ft3 bars per pier |
| Bearing at 2,000 psf | 1,571 lbper pier, presumptive soil |
The material list this produces
| Concrete, cu yd | 1 |
|---|---|
| Or 80 lb bags | 59 |
| Sonotube, 12 ft lengths | 5 |
| Rebar, ft | 115 |
| Rebar tie wire, lb | 1 |
| Post bases or anchor bolts | 9 |
Depth below grade compared
Depth swept with everything else held. The right hand column is the number of sonotubes, and it does not climb smoothly: 3 tubes hold for four rows and then jump to 5 and then to 9. Tubes come in 12 ft lengths and get cut, so what matters is how many whole piers fit in one.
| Depth below grade | Concrete to buy | 80 lb bags | Sonotube at 12 ft |
|---|---|---|---|
| 2 ft | 0.72 cubic yards | 33 | 3 |
| 2 ft 6 in | 0.86 cubic yards | 39 | 3 |
| 3 ft | 1.01 cubic yards | 46 | 3 |
| 3 ft 6 in | 1.15 cubic yards | 52 | 3 |
| 4 ft | 1.3 cubic yards | 59 | 5 |
| 5 ft | 1.58 cubic yards | 72 | 5 |
| 6 ft | 1.87 cubic yards | 85 | 9 |
What else matters here
Nine piers, 12 in round, 4 ft below grade with 6 in standing proud of it. That is 3.53 cu ft each, 1.3 cu yd in total, and it is the single most common deck footing layout there is.
The number people get wrong is the tubes. Each pier is 4.5 ft tall, a sonotube is 12 ft long, and two whole piers come out of one tube with 3 ft left over. So nine piers take 5 tubes, not 9. Divide instead of nesting and you order almost twice what the job needs, and the offcut is not returnable once it is cut.
That nesting is why the table below matters more than it looks. Tube count depends only on how tall the pier is, so it steps rather than climbing. At 3 ft 6 in below grade the piers are 4 ft tall, three fit in a tube, and nine piers take 3 tubes. Six inches deeper and only two fit, so the same nine piers take 5. Frost depth is published by your building department and is not a choice, but it is worth knowing that the extra six inches costs two tubes and not a fifth of one.
At 1.3 cu yd this is right on the line where bags stop making sense. Fifty nine eighty pound bags is 4,720 lb of material to buy, carry and mix, and a short load from a ready mix truck is usually cheaper and always faster. The calculator prints both so the trip can be priced as well as the concrete.
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 deck footing?
A 12 in round pier 4 ft below grade with 6 in above is 3.53 cu ft, which is about 6 eighty pound bags. Nine of them is 1.3 cu yd or 59 bags.
How many sonotubes do I need for nine deck footings?
Five. Each pier is 4.5 ft tall and a tube is 12 ft, so two whole piers come out of one tube. Dividing instead of nesting would have you buy nine.
How deep should deck footings be?
Below the frost line, and the frost depth where you are building is published by your building department rather than decided here. The table shows what each depth costs in bags and tubes once you know the number.
The concrete footing calculator takes any dimensions you like and hands back the same list.