Sonotube calculator: bags of concrete per tube form
Enter the tube diameter, how deep the concrete goes and how many tubes you have to see the bags per tube and in total.
Enter your measurements
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)
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
- 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.
Quick answers for common sizes
| Example | Answer |
|---|---|
| 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 |
| How many bags of concrete for an 8 inch Sonotube | 4 bags of 60 lb for a tube 4 ft deep |
Bags per tube by diameter (depth and bag as above)
| Tube diameter | Bags per tube | Concrete per tube | Bags of mix |
|---|---|---|---|
| 6 in | 1.4 bags | 0.82 cu ft | 2 bags |
| 8 in | 2.4 bags | 1.47 cu ft | 3 bags |
| 10 in | 3.8 bags | 2.29 cu ft | 4 bags |
| 12 in | 5.5 bags | 3.3 cu ft | 6 bags |
| 14 in | 7.5 bags | 4.49 cu ft | 8 bags |
| 16 in | 9.8 bags | 5.86 cu ft | 10 bags |
| 18 in | 12.4 bags | 7.42 cu ft | 13 bags |
| 24 in | 22 bags | 13.2 cu ft | 22 bags |
A tube form holds a cylinder of concrete, so the volume is just 3.1416 × radius² × height. For a 12 in tube that is 0.785 cu ft for every foot of depth — about 1⅓ bags of 80 lb per foot, the same figure Sonoco prints for its Builder’s Tube.
Concrete per foot of tube
| Tube diameter | Cu ft per foot | 80 lb bags per foot | 60 lb bags per foot | Cu yd for a 4 ft tube |
|---|---|---|---|---|
| 6 in | 0.196 | 0.33 | 0.44 | 0.029 |
| 8 in | 0.349 | 0.58 | 0.78 | 0.052 |
| 10 in | 0.545 | 0.91 | 1.21 | 0.081 |
| 12 in | 0.785 | 1.31 | 1.75 | 0.116 |
| 14 in | 1.069 | 1.78 | 2.38 | 0.158 |
| 16 in | 1.396 | 2.33 | 3.10 | 0.207 |
| 18 in | 1.767 | 2.95 | 3.93 | 0.262 |
| 24 in | 3.142 | 5.24 | 6.98 | 0.465 |
The Sonotube sizes chart lists every standard diameter with cubic yards at Sonoco’s column heights.
Worked examples
- How many bags of concrete for a 12 inch Sonotube — the common deck pier, 4 ft deep.
- How many bags of concrete for a 10 inch Sonotube — smaller decks, porch posts and pergolas.
- How many bags of concrete for an 8 inch Sonotube — light posts, signs and fence piers.
What the calculator won’t decide
How wide the pier must be, how deep it goes, whether it sits on a wider spread footing and whether it needs rebar are all set by your deck plans and local building code — and in cold climates the bottom usually has to be below the frost line. Enter what those call for and the calculator counts the bags. If your plans show a spread footing under the tube, add it with the footing calculator.
Filling tubes well
- Brace each tube plumb with stakes and screws before filling; a full tube is heavy and won’t move once it starts to set.
- Backfill and tamp soil around the outside of the tube before pouring so the cardboard doesn’t bulge.
- Fill in lifts of a foot or two and rod or tap the tube to settle the concrete and push out air pockets.
- Set the post base or anchor bolt while the concrete is still soft, checking its height and position against a string line.
- Cardboard above grade can be peeled off once the concrete has hardened; below grade it is usually left to rot away.
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) - Post hole diggerMid-range price
Digs neat, straight-sided holes. For more than a dozen holes, rent a powered auger and use this to clean them out.
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 much concrete is in a 12 inch Sonotube per foot?
0.785 cu ft per foot of height — 3.1416 × 0.5² — or about 1.3 bags of 80 lb. Sonoco’s Builder’s Tube table puts it at 1⅓ bags per foot.
What sizes do Sonotubes come in?
Sonoco’s round tubes come in diameters from 6 to 36 in in a standard 12 ft length; its Builder’s Tube for DIY comes in 6, 8, 10 and 12 in at 4, 8 and 12 ft. Quikrete’s QUIK-TUBE is 8, 10 or 12 in in 4 ft lengths. See the Sonotube sizes chart.
Should I add extra concrete for a tube?
A little. The tube itself holds a precise volume, but the hole below and around the bottom is rarely clean. 5% covers spillage; add more if the hole is dug wider than the tube for the bottom foot or so.
Can I use fast-setting concrete in a Sonotube?
Yes, Quikrete’s fast-setting mix comes in 50 lb bags yielding about 0.375 cu ft. Mix it wet in a tub for tubes rather than dry-pouring it, so you can fill and consolidate the whole tube before it sets in 20–40 minutes.
Related guides
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.