Box section sizes and which one to use where

Box sections are the most widely used item in steel structures. The difference between two sizes that appear to do the same job usually hides in the wall thickness; the wrong choice means either unnecessary cost or a frame that does not carry.

Standard size range

Square box sections are commonly available from 20×20 mm up to 200×200 mm. Rectangular sections range from 20×40 to 100×200. Wall thickness runs from 1.2 mm to 6.0 mm and the standard length is 6 metres.

S235JRH is the common grade for structural work, produced to EN 10219. Galvanised box sections typically carry around 275 g/m² of zinc coating, to EN 10346.

Which size goes where

20×20 – 30×30 mm: Light work. Garden fencing, pergolas, greenhouse frames, furniture and interior partitions.

40×40 – 50×50 mm: Railings, stair handrails, light canopies and sign supports. This is the range asked for most often.

60×60 – 80×80 mm: Car park canopies, light steel truss members, secondary columns.

100×100 mm and above: Load-bearing columns and beams, steel warehouse and factory frames. At these sizes wall thickness and grade belong to the structural calculation, not to guesswork.

Why wall thickness matters more than size

The same 50×50 profile is made in 1.5 mm and in 3 mm. They look identical from the outside but differ in load capacity and weight. Stating wall thickness alongside the size removes surprises on site.

Give the size and the wall thickness together — "a 50 profile" alone does not describe an order.

Black or galvanised

For enclosed spaces and work that will be painted afterwards, black section is enough. Outdoors, in damp areas or anywhere exposed to sea air, galvanised is the choice. In coastal districts such as Alanya this decision directly sets the life of the structure.

Our Alanya warehouse carries the common square and rectangular sizes in both black and galvanised, cut to the length you need. Send us the size and quantity and we can confirm stock the same day.