How many bags of concrete for a 10 inch sonotube?

4 bags of 80 lb for a 4 ft tube, 3 for 3 ft and 2 for 2 ft, with 10% waste. In 50 lb fast-setting bags: 7, 5 and 4. A 10 inch tube holds 0.55 cubic feet per foot of length.

How many bags of concrete for a 12 inch sonotube?

6 bags of 80 lb at 4 ft, 5 at 3 ft, 3 at 2 ft. A 12 x 48 inch tube is the common deck footing in frost areas and it is right at the point where mixing by hand gets tedious: six of them is 36 bags.

How many bags of concrete for an 8 inch sonotube?

2 bags of 80 lb or 4 of 50 lb at 3 ft; 3 and 5 at 4 ft. Eight inch tubes suit light posts and small decks; check that the tube diameter is at least three times the post or bracket width.

How much concrete is in a sonotube per foot?

0.35 cubic feet per foot for 8 inch, 0.55 for 10 inch, 0.79 for 12 inch and 1.4 for 16 inch. Multiply by the length in feet, add 10%, divide by the bag yield (0.60 cubic feet for 80 lb) and round up.

Do I add the footing at the bottom of the tube?

If the tube sits on a wider footing (a bell or a square pad below frost depth, required by many codes), that concrete is extra: work it out as a slab or a second, wider cylinder in the calculator. The tables are for the tube only. Check local code for the footing size and the depth below frost.

Should I mix by hand or order ready-mix for sonotubes?

Up to about 30 bags, mix; above that, or if the tubes are far from the driveway, price a small ready-mix load. Six 12 inch tubes at 4 ft are 36 bags of 80 lb, or about 0.8 cubic yards, which most plants will deliver with a short-load fee.

How many bags of concrete for a sonotube? 8, 10, 12 and 16 inch

A 10 inch sonotube 4 ft long holds 2.18 cubic feet of concrete; with 10% waste that is 4 bags of 80 lb, 6 of 60 lb or 7 of 50 lb. A 12 inch tube at the same depth takes 6 bags of 80 lb, and an 8 inch tube 3 ft deep only 2. The tables give 8, 10, 12 and 16 inch tubes at 2, 3 and 4 ft, the concrete per foot of tube, and the metric forms in 25 kg bags.

Open the concrete calculator

Bags per sonotube by diameter and length

A sonotube is a cardboard cylinder that is filled to the top, so the concrete is the full volume of the tube: pi x (diameter / 2)² x length. The tables include 10% waste, because tubes are often cut a little long and the bottom is never quite level, and use the yields printed on typical bags: 0.60 cubic feet for 80 lb, 0.45 for 60 lb and 0.375 for 50 lb fast-setting mix.

8 inch sonotube (0.35 cu ft per foot), 10% waste
Length	Concrete (cu ft)	With waste (cu ft)	80 lb bags	60 lb bags	50 lb bags
2 ft	0.7	0.77	2	2	3
3 ft	1.05	1.15	2	3	4
4 ft	1.4	1.54	3	4	5

10 inch sonotube (0.55 cu ft per foot), 10% waste
Length	Concrete (cu ft)	With waste (cu ft)	80 lb bags	60 lb bags	50 lb bags
2 ft	1.09	1.2	2	3	4
3 ft	1.64	1.8	3	4	5
4 ft	2.18	2.4	4	6	7

12 inch sonotube (0.79 cu ft per foot), 10% waste
Length	Concrete (cu ft)	With waste (cu ft)	80 lb bags	60 lb bags	50 lb bags
2 ft	1.57	1.73	3	4	5
3 ft	2.36	2.59	5	6	7
4 ft	3.14	3.46	6	8	10

16 inch sonotube (1.4 cu ft per foot), 10% waste
Length	Concrete (cu ft)	With waste (cu ft)	80 lb bags	60 lb bags	50 lb bags
2 ft	2.79	3.07	6	7	9
3 ft	4.19	4.61	8	11	13
4 ft	5.59	6.14	11	14	17

Concrete per foot of tube

For a length that is not in the tables, take the per-foot figure and multiply. The bag columns here are per foot with waste, not rounded, so you round once at the end for the whole tube.

Per foot of tube, 10% waste, bags not rounded
Diameter	Cu ft per foot	80 lb bags per foot	50 lb bags per foot
8 in	0.35	0.6	1
10 in	0.55	1	1.6
12 in	0.79	1.4	2.3
16 in	1.4	2.6	4.1

How the numbers are worked out

Radius squared times pi times length, all in feet: a 10 inch tube has a radius of 5 inches, or 0.417 ft, so 0.417² x 3.1416 x 4 = 2.18 cubic feet for 4 ft. Add 10%, divide by the bag yield, round up. The concrete calculator does this in the post hole or column mode for any diameter, and multiplies by the number of tubes.

A deck on six tubes

A typical small deck stands on six 12 inch tubes 4 ft deep in a frost area: 6 x 6 = 36 bags of 80 lb, about 1.4 US tons of dry mix. That is a full day of mixing for two people; a ready-mix truck fills the same tubes in half an hour. The bagged versus ready-mix article has the arithmetic for your local prices.

Metric: 200, 250 and 300 mm forms

Cardboard forms are sold in 200, 250 and 300 mm diameters; 25 kg bags yield about 12 litres of concrete.

Round forms, 10% waste
Diameter	Depth	Concrete (L)	25 kg bags
200 mm	600 mm	19	2
200 mm	900 mm	28	3
200 mm	1200 mm	38	4
250 mm	600 mm	29	3
250 mm	900 mm	44	5
250 mm	1200 mm	59	6
300 mm	600 mm	42	4
300 mm	900 mm	64	6
300 mm	1200 mm	85	8

Before you pour

Tube diameter: at least three times the width of the post or the bracket it will carry, and never less than 8 inches for anything structural.
Set the tube plumb on compacted gravel or on the footing, backfill around it before pouring so it does not float or bulge, and fill in one go, rodding the concrete every foot to knock out air pockets.
Push the post anchor or the J-bolt into the wet concrete at the right height and check it with a string line before it sets.
Fence posts set directly in the ground, without a tube, are in the fence post guide.

Frequently asked questions

How many bags of concrete for a 10 inch sonotube?: 4 bags of 80 lb for a 4 ft tube, 3 for 3 ft and 2 for 2 ft, with 10% waste. In 50 lb fast-setting bags: 7, 5 and 4. A 10 inch tube holds 0.55 cubic feet per foot of length.
How many bags of concrete for a 12 inch sonotube?: 6 bags of 80 lb at 4 ft, 5 at 3 ft, 3 at 2 ft. A 12 x 48 inch tube is the common deck footing in frost areas and it is right at the point where mixing by hand gets tedious: six of them is 36 bags.
How many bags of concrete for an 8 inch sonotube?: 2 bags of 80 lb or 4 of 50 lb at 3 ft; 3 and 5 at 4 ft. Eight inch tubes suit light posts and small decks; check that the tube diameter is at least three times the post or bracket width.
How much concrete is in a sonotube per foot?: 0.35 cubic feet per foot for 8 inch, 0.55 for 10 inch, 0.79 for 12 inch and 1.4 for 16 inch. Multiply by the length in feet, add 10%, divide by the bag yield (0.60 cubic feet for 80 lb) and round up.
Do I add the footing at the bottom of the tube?: If the tube sits on a wider footing (a bell or a square pad below frost depth, required by many codes), that concrete is extra: work it out as a slab or a second, wider cylinder in the calculator. The tables are for the tube only. Check local code for the footing size and the depth below frost.
Should I mix by hand or order ready-mix for sonotubes?: Up to about 30 bags, mix; above that, or if the tubes are far from the driveway, price a small ready-mix load. Six 12 inch tubes at 4 ft are 36 bags of 80 lb, or about 0.8 cubic yards, which most plants will deliver with a short-load fee.

How many bags of concrete for a 10x10 slab?
Bags of 80, 60 and 40 lb concrete for a 10 x 10 ft slab at 4, 5 and 6 inches with 10% waste, plus the metric 3 x 3 m version in 25 kg and 20 kg bags.
How many bags of concrete per fence post?
Bags of 80, 60 and 50 lb concrete per 4x4 or 6x6 fence post for 8, 10 and 12 inch holes at 24, 30 and 36 inches deep, plus the metric 100 mm post in 25 kg bags.
How many bags of concrete in a cubic yard?
80, 60, 50 and 40 lb bags per cubic yard and per cubic foot, 25 kg and 20 kg bags per cubic metre, what a yard of bags weighs, and when a ready-mix truck makes sense.
How much concrete for a 12x12 slab? (plus 16x16, 20x20, 24x24)
Cubic yards and bags of concrete for 12x12, 16x16, 20x20 and 24x24 ft slabs at 4 and 6 inches with 10% waste, the 4 x 4 m metric slab, and the point where ready-mix wins.

Last updated 2026-09-12. Figures are planning estimates from typical product data: check the yield, size or coverage printed on what you buy and round up.