How do I calculate the volume of a concrete cylinder?

Volume = pi x radius² x height, where radius is half the diameter. For a 300 mm diameter, 900 mm tall cylinder: pi x 0.15² x 0.9 = 0.0636 m³. Multiply by the number of identical cylinders, then add a waste allowance, to get the total volume to order.

What size are standard concrete test cylinders?

ASTM C39/C31 QA test cylinders are commonly cast at 4 in x 8 in or 6 in x 12 in (diameter x height), with the larger 6x12 in size the traditional standard and the 4x8 in size increasingly common for its lighter weight and lower aggregate-size requirement.

Are round footings common on Gibraltar building sites?

Yes — bollard and fence-post footings poured with tube formwork are common on Gibraltar's small residential and commercial sites, where British-derived building practice generally applies alongside locally sourced or imported ready-mix concrete.

Concrete Cylinder Calculator — Volume & Test Cylinder Sizes | Gibraltar

Concrete Cylinder Calculator: Volume for Round Piers, Bollards & Footings

Not every concrete pour is a rectangular slab. Round footings, deck piers, fence-post and bollard footings, and standard ASTM test cylinders are all cylinders, and their volume math is different from a slab's. This calculator works out the exact volume from a cylinder's diameter and height, multiplies it for however many identical cylinders you are pouring, and converts the total into a bag count or a cement:sand:aggregate mix split, plus a material cost estimate — covering both site pours (piers, bollards) and QA test cylinders (4x8 in or 6x12 in).

How to use the concrete cylinder calculator

Enter the cylinder diameter and choose its unit (m, cm, ft or in), or pick a standard 4x8 in / 6x12 in test-cylinder preset.
Enter the cylinder height and choose its unit.
Set the quantity — how many identical cylinders you are pouring (e.g. 6 for a standard QA test batch).
Adjust the waste allowance if needed — 5-10% is typical.
Choose "Bags" for pre-mixed dry bags, or "Custom mix" for a site-batched cement:sand:aggregate ratio.
Read off the total volume, the bag count or mix-component volumes, and the estimated material cost.

The math behind the calculation

A cylinder's volume is pi x radius² x height, where radius is half the diameter — a different shape from a slab's simple length x width x thickness, so entering the diameter without halving it first is the most common mistake.

Worked example: a footing 300 mm (0.3 m) in diameter and 900 mm (0.9 m) tall. Radius = 0.15 m, so volume = pi x 0.15² x 0.9 = 0.0636 m³ per cylinder. For 4 identical footings, the raw total is 4 x 0.0636 = 0.254 m³. Adding a 5% waste allowance: 0.254 x 1.05 = 0.267 m³ to order. At a bag yield of 0.017 m³, that is 0.267 / 0.017 = 15.7, rounded up to 16 bags.

Pro tips

Always measure diameter, not radius — entering the radius by mistake understates the volume by a factor of four.

For ASTM C39/C31 QA test cylinders, pour the standard 4x8 in or 6x12 in preset size so strength results are comparable to code-required test data.

At a typical material cost of around £155 per m³ of ready-mix concrete (reflecting Gibraltar's import premium), four 300 mm x 900 mm footing cylinders (0.267 m³ including 5% waste) cost roughly £41 in raw material — formwork and labour are additional.