Circular Concrete Column Calculator

A circular column is the standard form for verandah posts, garage roof supports, jetty piles, footing piers, and many bridge and warehouse supports. The volume math is identical to a circular slab — π × radius² × height — but real-world columns add a few practical wrinkles around reinforcement and pour height.

How to measure

Measure the outside diameter of the formwork. For Sonotube or other prefabricated forms, the diameter is printed on the tube; verify it because formwork bows under wet concrete. For hand-built timber forms, measure across the actual interior at several points and average.

For height, measure from the top of the footing (or the starter-bar splice) to the soffit of the beam or slab the column will support. Don’t measure to the ground — the bottom of the column is often below grade.

How the calculation works

Volume is π × (diameter ÷ 2)² × height. The calculator converts every input into millimetres internally, computes the cubic-millimetre volume, then converts to your chosen output unit:

Metric: cubic metres (m³)
Imperial: cubic yards (yd³) and cubic feet (ft³)

A 10% buffer is added — the ACI 318 industry standard for waste, spillage, formwork bow and the strike-off cone at the top.

Worked example

A 400 mm diameter column, 3 m high:

radius = 0.2 m
volume = π × 0.2² × 3 = 0.377 m³
with 10% buffer = 0.415 m³

Pouring four of these on the same day is just under 1.7 m³ — comfortably within a single ready-mix delivery’s minimum.

Reinforcement and rebar volume

For typical columns reinforced at 1–2% of cross-section, the rebar displaces around 1% of the volume — well within the 10% buffer. Don’t bother subtracting it. For heavily reinforced columns (3%+ steel by volume — high-rise transfer columns, seismic detailing), do the cage volume math separately and adjust.

Pouring tall columns

Anything over about 1.5 m tall is best poured in lifts to control segregation and prevent the form from blowing out under hydrostatic pressure. Plan each lift:

Tall residential columns (3 m+): pour in two lifts with a 30-minute pause for initial set
Tall commercial columns: form ties at 600 mm centres, pour in lifts of 1.2 m or less

The volume calculation is the same; you just split the order across two trucks if needed.

On the jobsite

The Concrete Calculator app for iOS has this calculator plus four others (rectangular slabs, circular slabs, irregular slab area and post holes), saved projects, and full offline support. Get it on the App Store.

Frequently asked questions

How do I calculate concrete for a circular column?

Use π × (diameter ÷ 2)² × height. The calculator handles unit conversion and adds a 10% buffer per ACI 318. Same formula as a circular slab — the only difference is the depth becomes the column's full height.

What about reinforcement and the steel cage?

Standard practice is to ignore the volume of rebar — it displaces less than 1% of the concrete in a typical column and the 10% waste buffer easily absorbs it. Heavy reinforcement (above 4% steel by volume) starts to matter; subtract the cage volume manually if you're at that level.

How do I measure column height accurately?

Measure from the top of the footing or starter bars (not the ground) to the underside of the beam or slab the column will support. If you're forming the column in lifts, calculate each lift separately and add them.

Why add a 10% buffer to the volume?

A 10% waste factor accounts for spillage, formwork bow, the cone left on top of each column when struck off, and the small amount lost in pump lines. The American Concrete Institute (ACI 318) recommends 5–10%; 10% is the conservative default.

Can I use this for square columns?

No — this calculator is for round columns only. For square or rectangular columns, use a rectangular slab calculation with the column footprint as length × width and the column height as depth.