Sonotube calculator

How many bags of concrete your round tube forms, deck footings or post holes take.

Start from:

Tube or hole diameter in Depth of concrete ft How many tubes or holes Post set in the concrete Extra for spills and the hole bottom % Price (optional)

You need

24 bags of 80 lb concrete

or 60 lb bags: 31
or 50 lb bags: 37
or 40 lb bags: 47
Per tube: 3.14 cu ft (5.2 × 80 lb)
Total: 13.8 cu ft (0.51 yd³)
Weight (typical): 2,004 lb
Estimated cost

Bags from the yields printed on standard concrete mix; high-yield mixes make more, so check the bag. Footing size and depth come from your plans and local code; dig below the frost line where the ground freezes, and call 811 before you dig.

How to figure concrete for a Sonotube

A tube form is a cylinder, so its volume is the area of the circle times the depth. Take out the post if one is set in the concrete, multiply by the number of tubes, and divide by the bag's yield.

Circle area = π × (diameter ÷ 2)², in square inches
One tube = (circle area − post area) × depth (in) ÷ 1,728 = cubic feet
Total = one tube × number of tubes × (1 + extra ÷ 100)
Bags = total ÷ the bag's yield (0.60 cu ft for 80 lb), rounded up

Worked example

Your 12.0 in tube, 4.0 ft deep, holds 3.14 cu ft, or 5.2 bags of 80 lb. For 4 tubes with 10% extra that's 13.8 cu ft: 24 bags of 80 lb or 31 of 60 lb.

Concrete per foot of tube depth

Bags per foot of depth, no extra. Yields from the QUIKRETE Concrete Mix (No. 1101) data sheet, revised October 2022.

Diameter	Cu ft per ft	80 lb bags	60 lb bags
6 in	0.20	0.33	0.44
8 in	0.35	0.58	0.78
10 in	0.55	0.91	1.21
12 in	0.79	1.31	1.75
14 in	1.07	1.78	2.38
16 in	1.40	2.33	3.10
18 in	1.77	2.95	3.93
24 in	3.14	5.24	6.98

Sonotube questions

How many bags of concrete for a 12 in Sonotube?

1.31 bags of 80 lb per foot of depth, so a 12 in tube 4 ft deep takes 3.14 cu ft, about 5.2 bags: buy 6. The table above has other diameters.

How much concrete per fence post?

Using the concrete maker's fence-post method (a hole 3 times the post's width), a 4x4 post 3 ft deep sits in a 10.5 in hole that takes 1.55 cu ft around the post, about 2.6 bags of 80 lb. The fence calculator counts the posts and bags for a whole fence.

How deep should deck footings be?

Below your area's frost line, and as deep and wide as your plans and local code require; the building department can tell you both. Enter that depth above. A footing that stops above the frost line can heave when the ground freezes.

Should I use bags or ready-mix for Sonotubes?

Bags are easiest for a few tubes you can fill by hand. For many large tubes, compare the bag total with a ready-mix price per yard (switch the price above to per yd³), and see the concrete cost calculator for short-load fees.

Do I subtract the post from the concrete?

Yes, if the post is set in the concrete: pick its size above and the calculator takes out a 3.5 in or 5.5 in square. For a post that sits on a bracket on top of the footing, choose "None".