Sonotube Size Chart

All three bag charts are the same arithmetic

I checked every printed cell in QUIKRETE's capacity table and Sakrete's 80 lb table against ceil(cylinder volume ÷ bag yield). All thirty-six cells match exactly — QUIKRETE's 60 lb and 80 lb tables across four diameters and four depths, and Sakrete's 80 lb table across five diameters and four depths. Not one cell carries a fudge factor, a waste allowance, or a product-specific adjustment. That audit is pinned by a test in this repo, so if the geometry or the cited bag yields ever change, the check fails rather than the page quietly going stale.

This matters more than it sounds. It means you do not need the chart for the tube you own — you need π, the bag yield off the sack, and a ceiling function. It also means a chart that disagrees with the geometry is telling you something else, and it is worth knowing what.

Where the published numbers do drift

Sonoco is the exception, because it publishes rates rather than whole bags. Its cubic-foot figures are the geometry rounded up to two decimals — 0.80 for a 12″ tube against 0.785 exact, about 1.9% heavy. Harmless. The bag rates drift further: Sonoco lists 2 sixty-pound bags per foot for the same 12″ tube, where the arithmetic gives 1.745. That is 15% over.

On a single mailbox post that is one spare bag. On sixteen deck piers at 4 ft it is closer to eleven bags of concrete you bought and did not use, which is a real number of dollars and a real trip to return them. The fix is not to distrust Sonoco — it is to treat a per-foot rate as a rate, do the multiplication at your actual depth, and round up once at the end instead of once per foot.

Footing bases, and what fits what

A bell-shaped plastic footing form widens the bearing area at the bottom of a pier and gets poured at the same time as the column. Sonoco publishes both the fit and the concrete volume, which is the one genuine size-compatibility table in this whole category:

• Tube Base TB 22 footing form (fits 8" and 10" Sonotube forms) — adds 2 cubic feet of concrete
• Tube Base TB 28 footing form (fits 8", 10" and 12" Sonotube forms) — adds 4.5 cubic feet of concrete
• Tube Base TB 32 footing form (fits 12", 14", 16" and 18" Sonotube forms) — adds 7 cubic feet of concrete

Note how much that adds. A TB 32 base is 7 ft³ on its own — more concrete than 8.9 feet of the 12″ column sitting on top of it. If you are pricing a pier and you forgot the base, you are not slightly under, you are about half under.

What this chart cannot tell you

Which diameter to use. That is the question behind most searches that land here, and it is not a size-chart question — it comes from the load above, the frost depth where you are, the bearing capacity of your soil, the deck or post hardware instructions, and whatever your building department wants stamped. A 12″ pier is not "usually fine"; it is fine or not depending on four things this page knows nothing about.

What the chart is for is the step after that decision: you have a diameter and a depth from the drawings or the permit, and you need to know what to buy. For that, the table above and the concrete calculator for form tubes will get you to a bag count you can check by hand. If you are setting fence posts rather than piers, the fence post depth guide covers the embedment side, which follows a different rule entirely.