Concrete Footing and Pier Calculator: Yards, Bags and Tubes
Diameter or pad size, depth below grade, how much stands above it and how many, and it returns the concrete both ways, the forms, the steel and the bearing. Tubes are nested out of a 12 foot length rather than divided into it, because a 4.5 foot pier gets two out of one tube.
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.
Worked example
These are the figures the calculator opens with and the answer it gives. Change anything above and every number below moves with it.
- 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 |
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.
Diameter moves more than depth does
Nine 12 inch piers, 4 feet below grade with 6 inches standing above, is 3.53 cubic feet each and 1.3 cubic yards in total. Drop to 8 inch tubes and the same nine piers would be well under half of that, because the section area falls from 0.785 square feet to 0.349.
Depth is the linear term and diameter is the squared one. Taking those 12 inch piers from 4 feet down to 3 feet only moves a single pier from 3.53 to 2.75 cubic feet, a fifth less, while going from 12 inch to 8 inch cuts the same pier by more than half.
That matters at the bag shelf. Nine 12 inch piers is 78 sixty pound bags or 59 eighty pound bags, which is a pallet and a long afternoon. Six 8 inch piers is 18 eighty pound bags, which is a pickup load. The calculator prints both bag sizes so you can price the trip as well as the concrete.
Tubes are nested, not divided
Sonotube comes in 12 foot lengths and a pier is almost never 12 feet. A 4.5 foot pier gets two out of one tube, so nine of them need 5 tubes, not 9. A 3.5 foot pier gets three out of a tube, so four of those need 2 tubes.
Divide instead of nesting and you order one tube per pier, which is roughly double what the job takes on any normal footing depth. It is the same mistake the rebar list makes when it divides linear feet by stock length, and this calculator handles both the same way.
A square pad does not use a tube at all, so the row changes to form board when you switch the shape. Four 24 inch pads want 32 linear feet of form board, four sides of each, rather than a tube count that would mean nothing.
Bearing is the number nobody checks
A 12 inch pier on presumptive 2,000 pound soil carries about 1,571 pounds. An 8 inch one carries 699. A 24 inch square pad carries 8,000. Those are wildly different footings and they all take about the same afternoon to dig.
Two thousand pounds per square foot is the conservative presumptive value the code tables allow for ordinary soil without a test. Your actual soil can be better or a great deal worse, and a soils report or the building department is the only way to know which.
The point of the row is the comparison rather than the absolute number. If a deck post is carrying 2,500 pounds and the pier under it is good for 1,571, the answer is a bigger diameter or a pad under the pier, and it is cheaper to learn that before the concrete truck is booked.
Frost, steel and what goes on top
A warning appears whenever the depth is under three feet, because three feet is below the frost line only in the warmest parts of the country. A pier that stops short of frost depth lifts every winter and takes the deck, the porch or the shed with it. Your building department publishes the number for your county.
Vertical steel scales with the tube. Under 10 inches the list puts in two bars, 10 to 16 inches gets three and anything larger gets four, all stopped 3 inches short of the top for cover. Nine 12 inch piers is 115 linear feet of bar, and four 24 inch pads is 12 feet.
Post bases are one per pier and they are the cheapest part of the list and the one most often forgotten until the concrete has gone off. Set them wet or use an anchor bolt, but decide before the pour rather than drilling into green concrete afterward.
Questions people ask
How much concrete is in a 12 inch sonotube?
A 12 inch tube is 0.785 square feet of section, so every foot of depth is 0.785 cubic feet. A pier 4 feet below grade with 6 inches above is 4.5 feet tall and holds 3.53 cubic feet, which is about six 80 pound bags.
How many sonotubes do I need?
Fewer than you have piers, because a 12 foot tube cuts into pieces. Nine piers at 4.5 feet take 5 tubes, two per tube. Four piers at 3.5 feet take 2 tubes, three per tube. Ordering one tube per pier is close to double what the job needs.
How deep should a deck footing be?
Below your local frost line, which the building department publishes and which is anywhere from a foot in the south to five feet or more in the north. Anything under three feet gets a warning here because it is below frost depth only in the warmest parts of the country.
How much weight can a 12 inch concrete pier hold?
About 1,571 pounds on presumptive 2,000 pound per square foot soil, against 699 for an 8 inch pier and 8,000 for a 24 inch square pad. Presumptive values are conservative table figures, and real soil needs a test or the building department to confirm.
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Common sizes, worked out
The same calculator with the numbers already filled in, one page per size, each ending in its own material list.