Per unit
In an 8 in tube one 80 lb bag fills about 21 in of height, and a 60 lb bag about 15 in.
One cubic yard fills 19 of these columns.
Change the dimensions in the column calculator. Why every count rounds up: how many bags of concrete you need.
Column
Concrete for an 8 in sonotube, 4 ft tall
A single 8 in diameter round column (sonotube) 4 ft tall. The volume is the circle area π·(diameter/2)² times the height; multiply by the number of piers you are pouring. That is 1.4 cubic feet, or 0.05 cubic yards: 3 bags of 80 lb premix or 4 bags of 60 lb, before any waste.
Concrete needed
0.05cubic yards· 0.04 m³· 1.4 ft³
| Bag size | Bags needed |
|---|---|
| 40 lb | 5 |
| 60 lb | 4 |
| 80 lb | 3 |
| 25 kg | 4 |
| 30 kg | 3 |
Planning estimate, with no waste allowance included. Add 5-10% for spillage and over-excavation, and check the yield printed on your bag. Structural work must follow your local building code and an engineer's specification.
Bagged or ready-mix?
Bags
0.05 yd³ is under a ready-mix supplier's usual one-yard minimum, so bags are the answer whatever the price per yard says. Buy a couple more than the count above and return what you do not open.
Same job, other sizes
8 in sonotube
At this size
What changes on an 8 in sonotube, 4 ft tall
Mixing or ordering it
3 × 80 lb bags is 0.05 yd³ - a wheelbarrow-and-shovel job. Mix two bags at a time, keep the water tight to the bag's own figure, and place it in one go so there is no cold joint. No mixer, no delivery, no minimum load.
The dimensions used
| Diameter | 8 in |
|---|---|
| Height | 4 ft |
| Columns | 1 |
How it is worked out
A round column or sonotube form holds a cylinder of concrete: area π·(diameter/2)² times its height, multiplied by how many you are pouring. Enter the tube's inside diameter - that is the finished column diameter.
That volume - 1.4 ft³ - is divided by 27 to give 0.05 cubic yards, and by each bag's yield to give the bag count. An 80 lb bag of premix yields about 0.60 cubic feet, so this job takes 3 of them; bag counts always round up, because you cannot buy part of a bag.
Ordering ready-mix instead? Suppliers sell by the cubic yard (or cubic metre) and usually have a minimum load and a short-load surcharge - worth a call before you choose between bags and a truck.
Formwork
What is being measured
Nearby