At a glance
| Section | How it is written | Typical use in furniture | Behaviour worth knowing |
|---|---|---|---|
| SHS (square hollow section) | Square; size B × B and wall t | Legs, posts, frames, table bases | Same stiffness in both directions; the weld seam sits on one face |
| RHS (rectangular hollow section) | B × H and wall t | Rails, bench frames, shelf supports | Stiffer on the deep face: orient it to the load |
| CHS (circular hollow section) | Outside diameter D and wall t | Legs, rails, bar footrails, handrail-like tubes | No sharp corner to catch; needs a saddle cut at a joint |
| Flat bar | Width w and thickness t | Brackets, edge trims, skirting-like plinth bands, shelf supports | Stiff on edge, flexible flat: the same bar behaves very differently turned 90 degrees |
| Angle (L) | Leg a × a and thickness t | Edge protection, stiffening behind a panel, shelf brackets | Two flat legs make a ready-made fixing flange |
| Solid round or square bar | Diameter or side | Slim legs, rails, stretchers | Solid is heavier; sizes and finish are a partner call |
Practice summary, not a standard. Which sizes a partner workshop holds changes; ask before drawing one.
The shapes and how a size is written
Hollow sections are written with outside size first and wall thickness last: an SHS 40 × 40 × 3 is a 40 mm square with a 3 mm wall; an RHS 60 × 40 × 3 is 60 by 40 mm with the same wall; a CHS 42.4 × 2.6 is 42.4 mm outside diameter and 2.6 mm wall. Flat bar is width then thickness; an angle is leg by leg by thickness.
Two things in the notation matter more than they look. The wall thickness, not the outside size, sets the mass and much of the stiffness. And the outside corners of a hollow section are rounded: the standard for cold-formed welded hollow sections requires the corners to be rounded, so a ‘sharp’ square corner on a drawing is either a mitred joint, a solid bar or a machined detail.
The standards behind hollow sections, and their status
Cold-formed welded hollow sections are covered in the UK by BS EN 10219: Part 2 gives tolerances, dimensions and sectional properties. BSI lists BS EN 10219-2:2019, published 31 May 2019, as current; it replaced the 2006 edition, now withdrawn. BSI describes its scope as circular, square, rectangular and elliptical hollow sections up to 40 mm wall thickness. Hot-finished hollow sections are covered by BS EN 10210-2: the 2006 edition is withdrawn (16 May 2019) and listings show a 2019 edition as its replacement.
For furniture the practical difference is the process. Cold-formed sections are made from strip, rolled to shape and seam-welded; hot-finished sections are formed at temperature. Most furniture frames use cold-formed tube, but the schedule should say which standard and grade the workshop is working to, because a mill certificate, a stock size and a tolerance all follow from it. Part 1 of each standard covers delivery conditions and steel grades; we have not read it.
Common sizes and what a metre weighs
The tables list sizes that stockholders commonly list for light frames. Mass per metre is computed here from the nominal dimensions at 7.85 kg per litre of mild steel, ignoring the rounded corners and the standard’s tolerances, so it overstates a published mill figure by a few per cent. Published tables are the authority and are in the standard. Use ours to estimate how a frame will handle, ship and load a floor: for a worked total see the weight calculator sheet.
| Section | Outside size | Wall t (mm) | Mass, kg per m (computed) |
|---|---|---|---|
| SHS 20 × 20 × 2 | 20 × 20 mm | 2 | 1.13 |
| SHS 25 × 25 × 2 | 25 × 25 mm | 2 | 1.44 |
| SHS 30 × 30 × 2 | 30 × 30 mm | 2 | 1.76 |
| SHS 40 × 40 × 3 | 40 × 40 mm | 3 | 3.49 |
| SHS 50 × 50 × 3 | 50 × 50 mm | 3 | 4.43 |
| SHS 60 × 60 × 3 | 60 × 60 mm | 3 | 5.37 |
| SHS 80 × 80 × 4 | 80 × 80 mm | 4 | 9.55 |
| SHS 100 × 100 × 5 | 100 × 100 mm | 5 | 14.92 |
| RHS 40 × 20 × 2 | 40 × 20 mm | 2 | 1.76 |
| RHS 50 × 30 × 3 | 50 × 30 mm | 3 | 3.49 |
| RHS 60 × 40 × 3 | 60 × 40 mm | 3 | 4.43 |
| RHS 80 × 40 × 3 | 80 × 40 mm | 3 | 5.37 |
| RHS 100 × 50 × 4 | 100 × 50 mm | 4 | 8.92 |
| Section | Outside diameter | Wall t (mm) | Mass, kg per m (computed) |
|---|---|---|---|
| CHS 21.3 × 2.0 | 21.3 mm | 2.0 | 0.95 |
| CHS 26.9 × 2.3 | 26.9 mm | 2.3 | 1.40 |
| CHS 33.7 × 2.6 | 33.7 mm | 2.6 | 1.99 |
| CHS 42.4 × 2.6 | 42.4 mm | 2.6 | 2.55 |
| CHS 48.3 × 3.2 | 48.3 mm | 3.2 | 3.56 |
| CHS 60.3 × 3.2 | 60.3 mm | 3.2 | 4.51 |
| Section | Size (mm) | Mass, kg per m (computed) |
|---|---|---|
| Flat 20 × 3 | 20 wide × 3 thick | 0.47 |
| Flat 25 × 5 | 25 wide × 5 thick | 0.98 |
| Flat 40 × 5 | 40 wide × 5 thick | 1.57 |
| Flat 50 × 10 | 50 wide × 10 thick | 3.93 |
| Flat 75 × 10 | 75 wide × 10 thick | 5.89 |
| Angle 25 × 25 × 3 | 25 × 25, 3 thick | 1.11 |
| Angle 40 × 40 × 4 | 40 × 40, 4 thick | 2.39 |
| Angle 50 × 50 × 5 | 50 × 50, 5 thick | 3.73 |
| Angle 60 × 60 × 6 | 60 × 60, 6 thick | 5.37 |
The diameters shown are common pipe and tube sizes; confirm what a partner actually holds. Sections not listed here (stainless tube, precision tube, solid bar) have their own standards; for stainless grades see stainless 304 vs 316.
From section to frame: what the designer should decide
The section is the beginning of the specification, not the end. A frame is its section, its length and its joints, then the finish, and each of those has a decision attached.
- Section and orientation. Name the shape, size and wall thickness, and which face is deepest. An RHS laid flat and the same RHS on edge are different frames.
- Joints. Welded corners are ground and blended to the finish; a visible weld is a design decision. See weld finish and visible welds and tolerances for visible metalwork.
- Finish. The section and its corner radius affect how a coating wraps an edge: see powder coating metalwork and blackened, burnished and raw steel finishes.
- The load. A stone top, a bench for several people or a shelf bracket fixed to a wall is a structural question. Ask the partner workshop what section it recommends and, if it is a loaded piece, ask for an engineer’s sign-off. We do not publish a section-versus-span chart because it would be read as design.
- Plates and fixings. A base needs a way to meet the floor and the top. See fixings and fasteners.
Specification wording
Paste into your schedule or specification and replace anything in [square brackets] with your own figures. Wording is a starting point: your specification governs.
Frame of [ref] in [cold-formed welded steel hollow section to BS EN 10219, grade [S235JR / confirm with partner]]: legs [SHS 40 × 40 × 3], rails [RHS 50 × 30 × 3, deep face vertical], stretchers [flat bar 40 × 5]. Sizes are those on the approved shop drawing; the workshop confirms the sections it holds before ordering and submits mill certificates on request.
Corners of [ref] to be [mitred and welded, ground flush and blended to match the finish / butt-welded with the weld left visible as a detail / radiused by bending]. Weld finish to be approved on a sample, against the dated sample [date].
[Ref] carries [a stone top of [ ] kg / seating for [ ] persons / a wall-fixed shelf of [ ] kg]. The partner workshop proposes the section and fixing and submits an engineer's calculation or sign-off [name, date] before manufacture. Sections shown on this schedule are indicative until that sign-off is received.
Total frame mass [ ] kg, computed from the approved sections. The workshop confirms the mass in writing for handling and floor-loading checks.
Terms used on this page
- SHS, RHS, CHS
- Square, rectangular and circular hollow sections, written outside size first and wall thickness last.
- Wall thickness (t)
- The thickness of the steel wall of a hollow section, which sets its mass and much of its stiffness.
- Cold-formed
- Hollow sections made by rolling strip steel into shape at room temperature and welding the seam; the subject of BS EN 10219.
- Hot-finished
- Hollow sections formed at temperature; the subject of BS EN 10210.
- Mass per metre
- The weight of one metre of a section, used to estimate the weight of a frame.
Standards and sources
- BS EN 10219-2:2019: BSI Knowledge, read 7 Nov 2026: published 31 May 2019, Current; supersedes the 2006 edition (withdrawn). Not read.
- BS EN 10210-2: 2006 edition withdrawn 16 May 2019; 2019 edition current per BSI-linked listings. Not read.
Questions we are asked
What size steel tube should I use for table legs?
That depends on the top, the height and the use, and it is the workshop's call, not a chart on a website. Common choices for light frames are small square or circular hollow sections, but a stone top or a long unsupported span needs an engineer's view. Ask the partner workshop to propose the section and show the drawing.
What do the numbers in SHS 40 × 40 × 3 mean?
A square hollow section 40 mm by 40 mm outside, with a 3 mm wall. Outside size comes first and wall thickness last.
Why does the wall thickness matter more than the size?
Because the wall sets the mass and much of the stiffness. A 40 × 40 section with a 2 mm wall and one with a 4 mm wall look the same from outside but are very different frames.
Are corners on steel tube really square?
No. The outside corners of hollow sections are rounded, as the standard for cold-formed hollow sections requires. A sharp corner on a drawing means a mitred joint, solid bar or machining.
Which standard applies to steel tube for furniture?
Cold-formed welded hollow sections follow BS EN 10219 and hot-finished ones BS EN 10210. Ask the workshop which it is using and for the grade and mill certificate.
Download the factsheet
A two-page A4 PDF with the section shapes, a size and mass table, the notes on standards and wording for a frame schedule.