How many bags of concrete for an 8 inch Sonotube?
An 8 inch Sonotube 4 feet deep holds 1.4 cubic feet of concrete: 4 bags of 60 lb (3.3 bags exactly, with 5% extra) or 3 of 80 lb.
How to work it out
- 3.1416 × (8 in ÷ 2)² = 0.349 cu ft per foot × 4 ft = 1.4 cu ft
- + 5% = 1.47 cu ft ÷ 0.45 cu ft per 60 lb bag = 3.3 bags per tube
- One tube: buy 4 bags
Eight-inch tubes turn up under light posts — a mailbox, a sign, a deck stair landing post or a fence pier — where the load is small. They are also easy to set alone, which is why the 60 lb bag is used here.
Adjust for your project
More options: Extra
- Bags per tube
- 3.3 bags
- If you mix each tube separately, buy
- 4 bags · 60 lb bag
- Concrete per tube
- 1.47 cu ft (0.0543 cu yd)
- Or ready-mix, all tubes (incl. extra)
- 0.0543 cu yd (1.47 cu ft)
- Concrete per foot of tube
- 0.349 cu ft
- Weight of the concrete (≈ 145 lb/cu ft)
- 202 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.
8 inch tube at other depths (5% extra)
| Concrete depth in the tube | Bags per tube | Bags of mix | Concrete per tube |
|---|---|---|---|
| 2 ft | 1.6 bags | 2 bags | 0.73 cu ft |
| 3 ft | 2.4 bags | 3 bags | 1.1 cu ft |
| 4 ft | 3.3 bags | 4 bags | 1.47 cu ft |
| 5 ft | 4.1 bags | 5 bags | 1.83 cu ft |
Small tube, small numbers
At 0.349 cu ft per foot, an 8 in tube takes about 0.6 of an 80 lb bag per foot or 0.8 of a 60 lb bag — Sonoco’s Builder’s Tube table gives ⅗ of an 80 lb bag per foot. Quikrete’s QUIK-TUBE table puts an 8 in tube 4 ft deep at 3 bags of 80 lb or 4 of 60 lb, which matches the answer here.
Because the volume per tube is so small, rounding matters: one tube of 1.4 cu ft wastes most of a bag if you buy whole bags per tube. For a row of them, mix in a wheelbarrow and fill several tubes from each batch.
Mixing a small tube
A 60 lb bag mixes comfortably in a tub with a hoe, using about 4–7 pints of water (Quikrete’s range for that size). Fill the tube in two lifts and tap the sides to settle it. For a 4×4 mailbox post set straight in the ground instead, see how many bags of concrete for a mailbox post; for a bigger pier, how many bags of concrete for a 10 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) - 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) - Mortar hoeBudget price
The holes in the blade pull water through dry mix, so bagged concrete and mortar mix evenly without dry pockets.
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 80 lb bags for an 8 inch Sonotube?
3 bags of 80 lb for a 4 foot tube (2.4 bags exactly, with 5% extra).
How many bags for an 8 inch Sonotube 3 feet deep?
3 bags of 60 lb with 5% extra.
How many bags for four 8 inch Sonotubes?
14 bags of 60 lb sharing batches, or 16 bags mixing each tube separately.
Other common sizes
- How many bags of concrete for a 12 inch Sonotube — 6 bags of 80 lb for a tube 4 ft deep
- How many bags of concrete for a 10 inch Sonotube — 4 bags of 80 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.