How many bags of concrete for a 12 inch Sonotube?
A 12 inch Sonotube 4 feet deep holds 3.14 cubic feet of concrete. That is 6 bags of 80 lb (5.5 bags before rounding, with 5% extra) or 8 of 60 lb per tube.
How to work it out
- 3.1416 × (12 in ÷ 2)² = 0.785 cu ft per foot × 4 ft = 3.14 cu ft
- + 5% = 3.3 cu ft ÷ 0.6 cu ft per 80 lb bag = 5.5 bags per tube
- One tube: buy 6 bags
Twelve inches is the tube most deck plans and building departments show for small residential decks, and 4 ft is a common depth in places with moderate frost. Both numbers come from your plans; the bag math is below.
Adjust for your project
More options: Extra
- Bags per tube
- 5.5 bags
- If you mix each tube separately, buy
- 6 bags · 80 lb bag
- Concrete per tube
- 3.3 cu ft (0.12 cu yd)
- Or ready-mix, all tubes (incl. extra)
- 0.12 cu yd (3.3 cu ft)
- Concrete per foot of tube
- 0.785 cu ft
- Weight of the concrete (≈ 145 lb/cu ft)
- 456 lb (0 tons)
- Total to buy counts this as bags. Switch “How will you buy it?” to ready-mix truck if you are ordering a delivery.
- Call 811 (in the US) or your local utility locate service a few days before you dig.
12 inch tube at other depths (5% extra)
| Concrete depth in the tube | Bags per tube | Bags of mix | Concrete per tube |
|---|---|---|---|
| 2 ft | 2.7 bags | 3 bags | 1.65 cu ft |
| 3 ft | 4.1 bags | 5 bags | 2.47 cu ft |
| 4 ft | 5.5 bags | 6 bags | 3.3 cu ft |
| 5 ft | 6.9 bags | 7 bags | 4.12 cu ft |
| 6 ft | 8.2 bags | 9 bags | 4.95 cu ft |
| 8 ft | 11 bags | 11 bags | 6.6 cu ft |
1⅓ bags per foot
Every foot of a 12 in tube is 0.785 cu ft, which works out to 1.31 bags of 80 lb — Sonoco’s Builder’s Tube table rounds it to 1⅓. So a 3 ft tube takes 4 bags, a 4 ft tube a little over 5 (6 to buy), and a 5 ft tube 7. Quikrete’s QUIK-TUBE table gives the same 6 bags of 80 lb, or 7 of 60 lb with no spare, for a 12 in tube 4 ft deep.
A deck’s worth of tubes
A deck on nine piers at this size needs about 50 bags of 80 lb in total with the 5% extra — about 30 cu ft or 1.1 cubic yards, weighing roughly 4,200 lb once mixed. If you mix each tube separately you will buy 54, because each tube rounds up to 6. Mix in a wheelbarrow and share the last batch between two tubes to save a few bags. Over nine or ten tubes, a short load of ready-mix with a wheelbarrow crew can be easier, but the truck has to reach the yard.
Brace each tube plumb, backfill around it before filling and rod the concrete in lifts. Set the post base while the top is still soft. The smaller sizes are on how many bags of concrete for a 10 inch Sonotube and how many bags of concrete for an 8 inch Sonotube.
Different size? Use the full Sonotube Calculator.
What you’ll need
- Cardboard concrete tube formBudget price
Round fiber tubes form piers, columns and footings above or below grade. Sold in common diameters; cut to length with a handsaw.
See options on Amazon (opens in a new tab) - Post levelBudget price
Straps to a post or tube form and reads plumb in both directions at once, so you can set it while the concrete is still soft.
See options on Amazon (opens in a new tab) - Mortar and concrete mixing tubBudget price
A wide, shallow tub for one or two bags at a time — easier to clean and to pull a hoe through than a wheelbarrow.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How many bags of concrete for a 12 inch Sonotube 3 feet deep?
5 bags of 80 lb with 5% extra (4.1 bags exactly).
How many bags of concrete for nine 12 inch Sonotubes 4 feet deep?
50 bags of 80 lb if you share batches; 54 bags if you mix each tube on its own.
How many 60 lb bags for a 12 inch Sonotube?
8 bags of 60 lb for a 4 foot tube, with 5% extra.
Other common sizes
- How many bags of concrete for a 10 inch Sonotube — 4 bags of 80 lb for a tube 4 ft deep
- How many bags of concrete for an 8 inch Sonotube — 4 bags of 60 lb for a tube 4 ft deep
Sources
- Sonoco — Sonotube round concrete forms brochure (opens in a new tab) — Diameters 6 to 36 in; standard length 12 ft; concrete requirements in cubic yards by diameter and height.
- Sonoco — Sonotube Builder’s Tube concrete forms (opens in a new tab) — 6, 8, 10 and 12 in diameters in 4, 8 and 12 ft lengths; about 0.20, 0.35, 0.55 and 0.80 cu ft per foot of height.
- Quikrete QUIK-TUBE (No. 6922) data sheet (opens in a new tab) — 4 ft lengths in 8, 10 and 12 in diameters; 10 and 12 ft regionally.
- Quikrete Concrete Mix (No. 1101) data sheet (opens in a new tab) — Yields: 40 lb ≈ 0.30, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60, 90 lb ≈ 0.675 cu ft; unit weight ≈ 140 lb/cu ft; for pours 2 in thick or more; 6–9 pints of water per 80 lb bag; control joints every 6–8 ft; cure 5 days at 70 °F or above, 7 days at 50–70 °F; protect from freezing for 48 hours.
- 811 — Before You Dig (opens in a new tab) — The free national before-you-dig service; contact it a few business days before digging.