Over-excavation, spillage and uneven subgrade. 5-10% for formed work, 10-15% on rough ground.
Yields are the figures printed on the bag. Speciality mixes differ — check yours.
Optional. Leave at zero to skip the cost estimate.
Material quantity estimate for planning and purchasing. Not structural engineering advice, not a bid, and not a code determination.
Concrete per foot of tube
Round form volume is only ever πr²h, so the useful thing to have is the per-foot figure for standard tube diameters. Multiply by your depth and your count:
| Diameter | Per foot | Per foot (yd³) | 80 lb bags per foot |
|---|---|---|---|
| 6 in | 0.196 ft³ | 0.007 yd³ | 0.33 |
| 8 in | 0.349 ft³ | 0.013 yd³ | 0.58 |
| 10 in | 0.545 ft³ | 0.020 yd³ | 0.91 |
| 12 in | 0.785 ft³ | 0.029 yd³ | 1.31 |
| 16 in | 1.396 ft³ | 0.052 yd³ | 2.33 |
| 18 in | 1.767 ft³ | 0.065 yd³ | 2.95 |
| 24 in | 3.142 ft³ | 0.116 yd³ | 5.24 |
Sizing a deck footing
Pier diameter is set by the load each post carries and the bearing capacity of your soil, not by the post size. A deck post picks up the tributary area around it — roughly beam span times joist span divided by four for an interior post — and at 50 psf combined live and dead load that number tells you the bearing area you need.
Common residential results land on 12 inch tubes for modest decks and 16-24 inch for larger ones or poor soil, with a belled or spread base where required. The bottom of the pier goes below the frost line, same as any footing.
If the pour is tall, note that fresh concrete in a tall form exerts significant lateral pressure and the form needs bracing. Twelve inch tubes at 8 feet are routinely blown out by pours that were not braced.
Common questions
How much concrete in a 12 inch tube form?
0.785 cubic feet per foot of depth — so a 4 ft pier is 3.14 cubic feet, about 5.25 bags at 80 lb. Four of them is 12.6 cubic feet, or 0.47 cubic yards.
What size footing does a deck post need?
It depends on the tributary load and your soil bearing capacity. Twelve inch diameter is common for modest residential decks, 16-24 inch for larger spans or weak soil. Your building department will want the calculation or a prescriptive table.
How deep should a deck pier be?
Below the local frost line and bearing on undisturbed soil — 12 inches in warm regions, 42-48 inches across the northern US. The frost depth for your jurisdiction is published by your building department.