How much concrete does a sonotube hold?

A round column holds π × radius² × height. A 12-inch tube (6-inch radius) standing 4 feet takes π × 0.5² × 4 ≈ 3.14 cubic feet, about 0.12 yd³. Enter the tube diameter and height above and the volume, bag count and cubic-metre figure all update as you type.

Why is a round column less concrete than a square post?

Because a circle fits inside its bounding square with the corners left over — a circle fills about 78.5% of the square around it. A 12-inch round tube holds noticeably less than a 12-inch square form of the same height, which is why guessing from the box dimension over-orders every time.

How do I handle several piers at once?

Set the number of columns and the tool multiplies one tube by that count, assuming they are the same size. If your piers differ, run each size separately and add the results. The bag count and the ordered volume both reflect the total across every column.

Should I add waste for columns?

A little. Tube ends spill, the mix slumps as you rod it, and the very bottom of a bell or a footing pad under the tube swallows extra. Ten percent is a sensible start; on tall tubes filled from a barrow, nudge it up. It is the same reasoning as any pour — you cannot top up a column once it starts to set.

Concrete column calculator

This multiplies the circle of your tube by its height and by the number of piers. It does not size the pier or its footing for the load above — take that from an engineered detail or your plans. Treat the volume as an ordering estimate and confirm it with your supplier.

Enter the tube's inside diameter and the height you are filling, set how many piers of that size you have, and the tool returns the concrete in cubic yards and cubic metres, plus a bag count. A column is a cylinder, so the volume is the area of the circle times the height.

Worked example

A 12-inch sonotube filled to 4 feet: the radius is 6 inches, or 0.5 ft, so one tube is π × 0.5² × 4 ≈ 3.14 cubic feet, which is 3.14 ÷ 27 ≈ 0.12 yd³. Six of them is about 18.8 cubic feet, or 0.70 yd³; add 10% and you would order around 0.77 yd³, roughly 32 bags at 0.6 ft³ each.

The formula

volume = π × (diameter ÷ 2)² × height × columns

Diameter and height must share a unit before you multiply, so the tool drops the diameter into feet (or metres) first. The result is cubic feet, divided by 27 for cubic yards; in metric it is already cubic metres. Bags are the total volume over your per-bag yield.

What this tool assumes

Only that a full cylinder is π r² h and that 27 cubic feet make a yard — both definitions. The waste percentage and the bag yield are yours to set, because they are what genuinely varies from one job and one product to the next.

Questions

How much concrete does a sonotube hold?: A round column holds π × radius² × height. A 12-inch tube (6-inch radius) standing 4 feet takes π × 0.5² × 4 ≈ 3.14 cubic feet, about 0.12 yd³. Enter the tube diameter and height above and the volume, bag count and cubic-metre figure all update as you type.
Why is a round column less concrete than a square post?: Because a circle fits inside its bounding square with the corners left over — a circle fills about 78.5% of the square around it. A 12-inch round tube holds noticeably less than a 12-inch square form of the same height, which is why guessing from the box dimension over-orders every time.
How do I handle several piers at once?: Set the number of columns and the tool multiplies one tube by that count, assuming they are the same size. If your piers differ, run each size separately and add the results. The bag count and the ordered volume both reflect the total across every column.
Should I add waste for columns?: A little. Tube ends spill, the mix slumps as you rod it, and the very bottom of a bell or a footing pad under the tube swallows extra. Ten percent is a sensible start; on tall tubes filled from a barrow, nudge it up. It is the same reasoning as any pour — you cannot top up a column once it starts to set.

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