Concrete Tube Calculator
Concrete for cylindrical form tubes — deck footings, posts and piers — per tube and for the whole job.
Concrete for tube footings.
How the concrete tube calculator works
A form tube is a cylinder: πr²h. The trap is the units — tube diameters are quoted in inches or millimetres while depths are in feet or metres, and getting that wrong by a factor is the single most common ordering mistake.
A 250 mm tube 900 mm deep takes 44 litres, so a deck on twelve of them needs 0.53 m³ — comfortably a bagged job, but only just.
Formula: V = π (d/2)² h per tube
Worked examples
| Inputs | Total concrete | Note |
|---|---|---|
| Twelve 250 mm tubes, 900 mm deep | 0.583 | 0.58 m³ with waste |
| With a 2× bell footing | 0.886 | noticeably more |
| A single post | 0.093 | 93 litres |
FAQFrequently asked questions
How much concrete in a form tube?
A 250 mm tube takes about 49 litres per metre of depth; a 300 mm tube about 71 litres per metre.
How deep should footings go?
Below the frost line where there is one, and to bearing soil everywhere. Local code governs — 900 mm is common in temperate Australia, far deeper in cold climates.
What is a bell footing?
A flared base that spreads the load over more soil and resists frost heave lifting the pier out.
Should I order ready-mix for deck footings?
Twelve tubes is around 0.5 m³, which is under most minimum delivery charges. Bags usually win at that scale.
Do I leave the tube in place?
The buried part, yes. Trim the exposed portion flush after the pour — the cardboard degrades and looks poor.
Where these figures come from
- The Engineering ToolBox — material densities, coverage and unit data — bulk densities, concrete at 2,400 kg/m³, board and sheet sizes
- Brick Development Association — brick sizes and quantities — 215 × 102.5 × 65 mm, 60 bricks per m²
- UK Government — Approved Documents (Building Regulations) — Building Regulations guidance
Last checked: September 2026. Coverage rates and material sizes are typical manufacturer figures — check the product you buy.