How many bags of concrete for an 8 inch tube 2 feet deep?

Data checked October 2026

Short answer

An 8 in Sonotube 2 ft long holds 0.7 cu ft of concrete — 2 × 80-lb bags or 2 × 60-lb bags.

An 8 in tube holds 0.349 cu ft per foot: π × (8 ÷ 24 ft)² = 0.349; × 2 ft = 0.7 cu ft.
Quik-Tube's data sheet lists 2 × 80-lb or 2 × 60-lb per 4 ft tube — our 2 / 2 come from the same geometry.
Buy 2 × 80-lb bags with the usual 10% cushion (about $12.94).
Dig a 16 in hole (twice the tube) and buy 1 × 4 ft tube (about $10.88), cutting 2 columns from each.
Two feet suits fence-post sleeves and mailbox piers where frost is shallow.

Adjust it to your exact job

Tube size

Diameter

Sonotube sizes include 6, 8, 10, 12, 14, 16, 18, 24 in; Quik-Tube comes in 8, 10 and 12 in.

Exact diameter

= 8"

How many?

Concrete heightwhole tube

= 2' · 0.61 m

Above groundpart of it

= 6"

Footing under the tube

Pour a footing first

Quik-Tube method: 2 in of gravel, a 4–6 in footing as wide as the hole (2× the tube), then set the tube on it.

You need

2× 80-lb bags

1.2 bags per column · 0.03 yd³ including 10% extra · 160 lb

Per column: 0.7 ft³0.349 ft³ per foot of tube
Total concrete: 0.03yd³before waste
Hole to dig: 16in2× the tube diameter (Quik-Tube)
Bottom below grade: 1' 6"compare with your frost depth

Check against the tube makers

Bags per column, whole bags, no waste
Per column	60-lb	80-lb
This calculator (geometry)	2	2
Quik-Tube data sheet	2	2

All bag sizes for the job

Bags needed by size
Bag	Bags	Est. cost
40 lb · 0.3 ft³	3	—
50 lb · 0.375 ft³	3	—
60 lb · 0.45 ft³	2	$9.70
80 lb · 0.6 ft³	2	$12.94

Footing depth

Deck and porch footings must sit at least 12 in below undisturbed ground (IRC R507.3.2 / R403.1.4) and below your local frost depth. Builder's-grade tubes stay in place — Sonoco notes they are not designed to be stripped.

Timeline for standard 4000 psi mix

Walk on: 24 hours
Light loads / posts: 24 hours
Keep moist (cure): 5 days ≥70°F · 7 days at 50–70°F
Protect from freezing: 48 hours

Shopping list

2 bags Standard 4000 psi mix — 80-lb bags$12.94
1 tubes 8 in form tube, 4 ftcut 2 columns from each tube$10.88
1 pcs Post bases or anchor bolts, set in the wet concrete
3 gal Clean water for mixing2–2 gal; start low, never exceed the max

Estimated total$23.82

Cost estimate

Tap a price to use your store's

80-lb Standard 4000 psi mix
2 bags × $
$12.94
8 in × 48 in form tube
1 tubes × $
$10.88

Materials total$23.82

Typical U.S. big-box prices checked 2026. Tap any price to enter your store's.

Did this answer your question?

Compare

8 in tube at other lengths

Length	Cu ft per tube	80-lb per tube	60-lb per tube
2 ft ←	0.7	2	2
3 ft	1.05	2	3
4 ft	1.4	3	4
5 ft	1.75	3	4
6 ft	2.09	4	5
8 ft	2.79	5	7

How this was worked out

Round forms are cylinders: area = π × radius². An 8 in tube has a 4 in radius, so π × 4² = 50.3 sq in ÷ 144 = 0.349 sq ft. Multiply by the length in feet for cubic feet.

0.7 cu ft ÷ 0.6 cu ft per 80-lb bag = 1.16, and ÷ 0.45 per 60-lb bag = 1.55. Tube tables round each tube up — here that leaves most of a bag over, so on several tubes round the total instead.

At 0.03 yd³ this is a bag job: a truck's 1 yd minimum plus fees would cost about $485.

The full method, material data and tips are on the main sonotube & column concrete calculator page.

Similar jobs

Other sizes people check

Sources

Data behind this answer

Quikrete QUIK-TUBE Building Form No. 6922 — technical data sheet — Table 1 bags per 1–4 ft of 6/8/10/12 in tube; hole 2× tube diameter; 2 in gravel and a 4–6 in footing; brace at 2 ft above grade; up to 3 ft above grade · checked October 2026
Sonoco Sonotube Builder's Tube — bags per 4 ft: 8 in 4×60/3×80, 10 in 5/4, 12 in 8/6, 16 in 13/10; below grade and up to 3 ft above · checked October 2026
Home Depot Sakrete 48 in form tubes — price history (Glassit) — 8 in × 48 in $10.88, 10 in × 48 in $14.48 (Jul 13, 2026, one tracked store) · checked October 2026
Quikrete Concrete Mix No. 1101 — technical data sheet — bag yields (80 lb = 0.60 cu ft, 60 lb = 0.45, 50 lb = 0.375, 40 lb = 0.30), water per bag, curing times; post method: 6 in of dry mix in the hole bottom, 24 h before strain · checked October 2026
Home Depot & Lowe's listings — Quikrete 80 lb Concrete Mix — $5.98–$6.98 per 80-lb bag; $5.93 bulk tier at 42+ bags; 42 bags per pallet; Fast-Setting 50 lb $7.97 · checked October 2026
Published 2026 ready-mix plant price sheets (e.g. Gehring Concrete) — $146–$285 per yd³ before fees; short-load fees $50–$200 · checked October 2026
International Residential Code 2021 — R403.1 footings & Table R403.1(1) — 12 × 6 in minimum footing, width by soil bearing, 12 in below undisturbed ground, 3 in cover over bars cast against earth; deck footings R507.3 · checked October 2026

Short answer

An 8 in Sonotube 2 ft long holds 0.7 cu ft of concrete — 2 × 80-lb bags or 2 × 60-lb bags.

An 8 in tube holds 0.349 cu ft per foot: π × (8 ÷ 24 ft)² = 0.349; × 2 ft = 0.7 cu ft.

Quik-Tube's data sheet lists 2 × 80-lb or 2 × 60-lb per 4 ft tube — our 2 / 2 come from the same geometry.

Buy 2 × 80-lb bags with the usual 10% cushion (about $12.94).

Dig a 16 in hole (twice the tube) and buy 1 × 4 ft tube (about $10.88), cutting 2 columns from each.

Two feet suits fence-post sleeves and mailbox piers where frost is shallow.

Adjust it to your exact job

Tube size

Diameter

Sonotube sizes include 6, 8, 10, 12, 14, 16, 18, 24 in; Quik-Tube comes in 8, 10 and 12 in.

Exact diameter

= 8"

How many?

Concrete heightwhole tube

= 2' · 0.61 m

Above groundpart of it

= 6"

Footing under the tube

Pour a footing first

Quik-Tube method: 2 in of gravel, a 4–6 in footing as wide as the hole (2× the tube), then set the tube on it.

You need

2× 80-lb bags

1.2 bags per column · 0.03 yd³ including 10% extra · 160 lb

Per column: 0.7 ft³0.349 ft³ per foot of tube
Total concrete: 0.03yd³before waste
Hole to dig: 16in2× the tube diameter (Quik-Tube)
Bottom below grade: 1' 6"compare with your frost depth

Check against the tube makers

Bags per column, whole bags, no waste
Per column	60-lb	80-lb
This calculator (geometry)	2	2
Quik-Tube data sheet	2	2

All bag sizes for the job

Bags needed by size
Bag	Bags	Est. cost
40 lb · 0.3 ft³	3	—
50 lb · 0.375 ft³	3	—
60 lb · 0.45 ft³	2	$9.70
80 lb · 0.6 ft³	2	$12.94

Footing depth

Timeline for standard 4000 psi mix

Walk on: 24 hours
Light loads / posts: 24 hours
Keep moist (cure): 5 days ≥70°F · 7 days at 50–70°F
Protect from freezing: 48 hours

Shopping list

2 bags Standard 4000 psi mix — 80-lb bags$12.94
1 tubes 8 in form tube, 4 ftcut 2 columns from each tube$10.88
1 pcs Post bases or anchor bolts, set in the wet concrete
3 gal Clean water for mixing2–2 gal; start low, never exceed the max

Estimated total$23.82

Cost estimate

Tap a price to use your store's

80-lb Standard 4000 psi mix
2 bags × $
$12.94
8 in × 48 in form tube
1 tubes × $
$10.88

Materials total$23.82

Typical U.S. big-box prices checked 2026. Tap any price to enter your store's.

Length

Cu ft per tube

80-lb per tube

60-lb per tube

2 ft ←

0.7

3 ft

1.05

4 ft

1.4

5 ft

1.75

6 ft

2.09

8 ft

2.79

How this was worked out

Round forms are cylinders: area = π × radius². An 8 in tube has a 4 in radius, so π × 4² = 50.3 sq in ÷ 144 = 0.349 sq ft. Multiply by the length in feet for cubic feet.

0.7 cu ft ÷ 0.6 cu ft per 80-lb bag = 1.16, and ÷ 0.45 per 60-lb bag = 1.55. Tube tables round each tube up — here that leaves most of a bag over, so on several tubes round the total instead.

At 0.03 yd³ this is a bag job: a truck's 1 yd minimum plus fees would cost about $485.

The full method, material data and tips are on the main sonotube & column concrete calculator page.