How much concrete for a 18 inch Sonotube 4 feet long?

Data checked October 2026

Short answer

An 18 in Sonotube 4 ft long holds 7.07 cu ft of concrete — 12 × 80-lb bags or 16 × 60-lb bags.

An 18 in tube holds 1.767 cu ft per foot: π × (18 ÷ 24 ft)² = 1.767; × 4 ft = 7.07 cu ft.
Buy 13 × 80-lb bags with the usual 10% cushion (about $84.11).
Dig a 36 in hole (twice the tube) and buy 1 × 4 ft tube.
18 in tubes are used for large porch columns and heavily loaded piers.

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

= 1' 6"

How many?

Concrete heightwhole tube

= 4' · 1.22 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

13× 80-lb bags

11.8 bags per column · 0.29 yd³ including 10% extra · 1,040 lb

Per column: 7.07 ft³1.767 ft³ per foot of tube
Total concrete: 0.26yd³before waste
Hole to dig: 36in2× the tube diameter (Quik-Tube)
Bottom below grade: 3' 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)	16	12

All bag sizes for the job

Bags needed by size
Bag	Bags	Est. cost
40 lb · 0.3 ft³	26	—
50 lb · 0.375 ft³	21	—
60 lb · 0.45 ft³	18	$87.30
80 lb · 0.6 ft³	13	$84.11

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

13 bags Standard 4000 psi mix — 80-lb bags$84.11
1 tubes 18 in form tube, 4 ft
1 pcs Post bases or anchor bolts, set in the wet concrete
15 gal Clean water for mixing10–15 gal; start low, never exceed the max

Estimated total$84.11

Cost estimate

Tap a price to use your store's

80-lb Standard 4000 psi mix
13 bags × $
$84.11

Materials total$84.11

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

Did this answer your question?

Compare

18 in tube at other lengths

Length	Cu ft per tube	80-lb per tube	60-lb per tube
2 ft	3.53	6	8
3 ft	5.3	9	12
4 ft ←	7.07	12	16
5 ft	8.84	15	20
6 ft	10.6	18	24
8 ft	14.14	24	32

How this was worked out

Round forms are cylinders: area = π × radius². An 18 in tube has a 9 in radius, so π × 9² = 254.5 sq in ÷ 144 = 1.767 sq ft. Multiply by the length in feet for cubic feet.

7.07 cu ft ÷ 0.6 cu ft per 80-lb bag = 11.78, and ÷ 0.45 per 60-lb bag = 15.71. Tube tables round each tube up.

At 0.29 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 18 in Sonotube 4 ft long holds 7.07 cu ft of concrete — 12 × 80-lb bags or 16 × 60-lb bags.

An 18 in tube holds 1.767 cu ft per foot: π × (18 ÷ 24 ft)² = 1.767; × 4 ft = 7.07 cu ft.

Buy 13 × 80-lb bags with the usual 10% cushion (about $84.11).

Dig a 36 in hole (twice the tube) and buy 1 × 4 ft tube.

18 in tubes are used for large porch columns and heavily loaded piers.

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

= 1' 6"

How many?

Concrete heightwhole tube

= 4' · 1.22 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

13× 80-lb bags

11.8 bags per column · 0.29 yd³ including 10% extra · 1,040 lb

Per column: 7.07 ft³1.767 ft³ per foot of tube
Total concrete: 0.26yd³before waste
Hole to dig: 36in2× the tube diameter (Quik-Tube)
Bottom below grade: 3' 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)	16	12

All bag sizes for the job

Bags needed by size
Bag	Bags	Est. cost
40 lb · 0.3 ft³	26	—
50 lb · 0.375 ft³	21	—
60 lb · 0.45 ft³	18	$87.30
80 lb · 0.6 ft³	13	$84.11

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

13 bags Standard 4000 psi mix — 80-lb bags$84.11
1 tubes 18 in form tube, 4 ft
1 pcs Post bases or anchor bolts, set in the wet concrete
15 gal Clean water for mixing10–15 gal; start low, never exceed the max

Estimated total$84.11

Cost estimate

Tap a price to use your store's

80-lb Standard 4000 psi mix
13 bags × $
$84.11

Materials total$84.11

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

3.53

3 ft

5.3

4 ft ←

7.07

5 ft

8.84

6 ft

10.6

8 ft

14.14

How this was worked out

Round forms are cylinders: area = π × radius². An 18 in tube has a 9 in radius, so π × 9² = 254.5 sq in ÷ 144 = 1.767 sq ft. Multiply by the length in feet for cubic feet.

7.07 cu ft ÷ 0.6 cu ft per 80-lb bag = 11.78, and ÷ 0.45 per 60-lb bag = 15.71. Tube tables round each tube up.

At 0.29 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.