Form tubes / piers / bags
Sonotube Concrete Calculator
A 12 in tube 4 ft long holds 3.14 cu ft of concrete: 7 bags of 60 lb mix or 6 of 80 lb. Sonoco's table says 8 of 60 lb because it rounds the tube up to 0.8 cu ft a foot.
Sources checked
Your estimate
7 bags of 60 lb
3.14 cu ft (0.116 cu yd) in 1 tube.
- One tube3.14 cu ft
- 80 lb bags5.24 before rounding6 bags
- 50 lb bags8.38 before rounding9 bags
- 40 lb bags10.47 before rounding11 bags
Concrete needed for a Sonotube, pier or column
- The inside of a tube is a cylinder, and so is any round pier, column or caisson: pi x (diameter / 2)² x length. For 12 in and 4 ft: 3.1416 x 0.5² ft x 4 ft = 3.14 cu ft.
- Divide by the bag's yield and round up: 3.14 / 0.45 = 6.98, so 7 bags of 60 lb. For what each bag yields see how many cubic feet in a bag of concrete.
- Several tubes are added up first and rounded once; rounding each tube on its own can cost a bag more per tube. A footing that is not round, such as a slab or a step, goes through the concrete calculator.
diycalcs and CalcShed, run with no post in the hole, give 3.14 and 3.141 cu ft for the same tube, and both round to 7 bags of 60 lb.
Numbers we use
- One 60 lb bag yields
- 0.45 cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
- One 80 lb bag yields
- 0.6 cu ftQUIKRETE Concrete Mix 1101 data sheet (Oct 2022)
Tubes 4 ft long: our count beside the makers'
| Diameter | Cu ft per ft | Sonoco per ft | Ours, 60 / 80 lb | Sonoco, 60 / 80 lb | QUIK-TUBE, 60 / 80 lb |
|---|---|---|---|---|---|
| 6 in | 0.196 | 0.2 | 2 / 2 | Not printed | 2 / 2 |
| 8 in | 0.349 | 0.35 | 4 / 3 | 4 / 3 | 4 / 3 |
| 10 in | 0.545 | 0.55 | 5 / 4 | 5 / 4 | 5 / 4 |
| 12 in | 0.785 | 0.8 | 7 / 6 | 8 / 6 | 7 / 6 |
| 16 in | 1.396 | Not printed | 13 / 10 | 13 / 10 | Not printed |
Sources: Sonoco Sonotube Builder's Tube brochure (2016); QUIKRETE QUIK-TUBE 6922 data sheet (2018); Sonoco Sonotube Builder's Tube product page
Where sources disagree: 8 bags or 7
60 lb bags for a 12 in tube 4 ft long
- 8 bagsSonoco Sonotube Builder's Tube product page
- 7 bagsQUIKRETE QUIK-TUBE 6922 data sheet (2018)
- 1.7 bags a foot, 6.8 for 4 ftQUIKRETE project sheet: QUIK-TUBE Pillar Foundations
Sonoco prints 0.8 cu ft a foot for this tube where the geometry gives 0.785; 3.2 cu ft / 0.45 = 7.11, which rounds up to 8. QUIKRETE starts from the true volume, 3.14 / 0.45 = 6.98, and rounds to 7, as we do. For 80 lb bags both makers agree on 6.
Sonotube questions
How many bags of concrete fill a 12 inch Sonotube?
A 4 ft length takes 7 bags of 60 lb or 6 of 80 lb for its 3.14 cu ft. Each extra foot adds 0.785 cu ft.
How much concrete is in an 8 inch tube 4 feet long?
1.4 cu ft, which is 4 bags of 60 lb or 3 of 80 lb; Sonoco and QUIKRETE print the same two counts.
How many bags for a 10 inch form tube?
5 of 60 lb or 4 of 80 lb for 4 ft (2.18 cu ft), matching both makers' tables.
How do I calculate concrete for a cylinder, pier or column?
Square the radius in feet, multiply by pi and by the height. A 12 in pier 4 ft tall is 3.14 cu ft, 0.116 cu yd. Slabs and steps are on the concrete calculator; a round hole with a post standing in it is counted by the fence post concrete calculator.
How much does the concrete in a form tube weigh?
The 12 in tube 4 ft long holds 3.14 cu ft, about 440 lb at QUIKRETE's 140 lb per cubic foot.
How high above the ground can a form tube stand?
Up to 3 ft by QUIKRETE's QUIK-TUBE sheet and 3 ft on Sonoco's page. QUIKRETE asks for bracing once a tube stands 2 ft or more above the ground.
What lengths do Sonotube forms come in?
Sonoco's brochure lists 4, 8, 12 ft for its Builder's Tube; QUIK-TUBE is sold 4 ft long. A longer pier is one tube cut to length, and the calculator takes any length in feet.
A planning aid, not an engineering calculation: your local code and building inspector have the final word. Terms