Circular Hollow Section Weight, Section Properties, Steel Quantity and Cost Estimator
CHS (Circular Hollow Sections) — also known as steel tubes, round hollow sections, or structural steel pipes — are one of the most widely used structural steel profiles in UK construction, engineering, and fabrication in 2026. Their circular cross-section provides equal strength and stiffness in all directions (a key advantage over I-sections and rectangular hollow sections), making them the ideal choice for columns, bracing members, trusses, space frames, architectural features, and any structural application where loads arrive from multiple directions or where an aesthetically pleasing round profile is required.
CHS is manufactured to BS EN 10210 (hot-finished hollow sections) or BS EN 10219 (cold-formed hollow sections) and is designated by its outside diameter (OD) and wall thickness — for example, 168.3 × 10.0 CHS denotes a tube with a 168.3mm outside diameter and 10.0mm wall thickness. Standard steel grades for UK structural CHS are S275 (the most common for general structural use) and S355 (for higher strength applications). CHS is available in standard 6-metre and 12-metre mill lengths, with cut-to-length, profiled end preparation, and welded assembly available from UK steel stockholders and fabricators.
The mass per metre of CHS is the most fundamental property for structural steel quantity estimating and is calculated from the cross-sectional area of steel multiplied by the density of steel (7,850 kg/m³). For a CHS with outside diameter D and wall thickness t, the cross-sectional area A = π/4 × (D² – d²), where d = D – 2t is the inside diameter. The mass per metre = A × 7,850 / 10⁶ (converting mm² to m²). Standard UK CHS sizes have published mass per metre values in steel section tables per BS 4-2:2004 and the BCSA / SCI Steelwork Design Guide tables — used by structural engineers, quantity surveyors, and fabricators throughout the UK.
The second moment of area (I) governs the bending stiffness and deflection of CHS members under lateral loading. For a circular hollow section, I = π/64 × (D⁴ – d⁴). The elastic section modulus (Wel) = I / (D/2) determines the elastic bending capacity. The plastic section modulus (Wpl) = (D³ – d³) / 6 determines the plastic moment capacity used in plastic analysis and Class 1/2 sections to Eurocode 3. The radius of gyration (i) = √(I/A) governs buckling resistance in compression and combined loading — for CHS, the radius of gyration is the same in all directions, a major structural advantage over asymmetric sections.
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Structural columns are one of the most common applications for CHS in UK commercial and industrial buildings. The circular cross-section provides equal buckling resistance in all directions under axial compression, allowing efficient structural design with smaller section sizes than equivalent I-section or H-section columns of the same weight. CHS columns are particularly popular in open-plan commercial offices, retail units, sports facilities, and industrial sheds where the circular profile is architecturally desirable and where loads may arrive from multiple directions or change direction over the building's life.
Trusses and space frames extensively use CHS chord and web members throughout UK engineering and construction. The smooth circular profile facilitates the welded node connections required in triangulated CHS trusses, and CHS members can be profiled (cope-cut) at their ends to achieve tight geometric fit-up at welded joints without gusset plates. Bracing systems in multi-storey buildings frequently use circular hollow sections due to their symmetrical section properties — CHS bracing members carry equal tension and compression in reversal loading cycles, and their round cross-section is more aesthetically acceptable in exposed structural applications than flat plate or angle bracing.
Architectural exposed steelwork represents a growing application for CHS in UK construction, driven by the architectural trend for expressed structural frames in commercial offices, retail, education, and cultural buildings. CHS members have a naturally elegant appearance that suits contemporary architectural expression, and their smooth circular surface is easier to paint or coat than the complex flanges and webs of I-sections. Hot-dip galvanised or stainless steel CHS is widely used in external canopies, entrance structures, balcony railings, and glazed atrium frames where a maintenance-free or low-maintenance finish is required.
Circular hollow sections offer distinct advantages over rectangular (RHS) and square (SHS) hollow sections in specific applications, though each section type has its own strengths that determine the most appropriate choice for each structural element. The primary structural advantage of CHS over RHS/SHS is equal properties in all directions — the second moment of area, radius of gyration, and section modulus are identical in every axis, making CHS the most efficient section for columns under multi-directional loading and for bracing members subject to tension/compression reversal.
RHS and SHS offer easier connection details — bolting to the flat face of an RHS/SHS is considerably simpler than connecting to the curved surface of a CHS, and welding flat-section gussets and end plates is more straightforward. For multi-storey building frames where beam connections are made to column faces, RHS/SHS is often preferred for ease of detailing. CHS is preferred where the round profile is architecturally required, where connections are made by direct welding between CHS members (as in roof trusses and space frames), and where the equal stiffness in all directions is structurally efficient.
The following table provides section properties for the most commonly used CHS sizes in UK structural engineering in 2026. All values conform to BS EN 10210 hot-finished circular hollow sections and are calculated to the formulae in BS 4-2:2004 and the SCI/BCSA Steelwork Design Guide to BS EN 1993. Use the CHS calculator above for any size not listed here.
| CHS Size (OD × t) | Mass (kg/m) | Area A (cm²) | I (cm⁴) | Wel (cm³) | Wpl (cm³) | i (cm) |
|---|---|---|---|---|---|---|
| 48.3 × 3.2 | 3.56 | 4.53 | 10.8 | 4.47 | 6.04 | 1.54 |
| 60.3 × 3.2 | 4.51 | 5.74 | 21.4 | 7.10 | 9.44 | 1.93 |
| 76.1 × 3.2 | 5.75 | 7.33 | 43.5 | 11.4 | 15.1 | 2.44 |
| 76.1 × 5.0 | 8.77 | 11.2 | 63.5 | 16.7 | 22.6 | 2.39 |
| 88.9 × 3.2 | 6.76 | 8.62 | 70.0 | 15.7 | 20.7 | 2.85 |
| 88.9 × 5.0 | 10.3 | 13.2 | 103 | 23.2 | 31.2 | 2.80 |
| 114.3 × 5.0 | 13.5 | 17.2 | 219 | 38.3 | 51.1 | 3.57 |
| 114.3 × 6.3 | 16.8 | 21.4 | 266 | 46.5 | 62.6 | 3.52 |
| 139.7 × 5.0 | 16.6 | 21.2 | 401 | 57.4 | 76.3 | 4.35 |
| 139.7 × 6.3 | 20.7 | 26.4 | 493 | 70.6 | 94.4 | 4.32 |
| 168.3 × 5.0 | 20.1 | 25.7 | 706 | 83.9 | 111 | 5.24 |
| 168.3 × 6.3 | 25.2 | 32.1 | 875 | 104 | 139 | 5.22 |
| 168.3 × 10.0 | 38.7 | 49.3 | 1,290 | 153 | 209 | 5.12 |
| 193.7 × 6.3 | 29.1 | 37.1 | 1,330 | 137 | 182 | 5.99 |
| 193.7 × 10.0 | 45.3 | 57.7 | 1,980 | 205 | 278 | 5.85 |
| 219.1 × 6.3 | 33.1 | 42.1 | 1,930 | 176 | 234 | 6.77 |
| 219.1 × 10.0 | 51.6 | 65.7 | 2,900 | 265 | 357 | 6.65 |
| 273.0 × 8.0 | 52.3 | 66.6 | 5,900 | 432 | 572 | 9.42 |
| 273.0 × 10.0 | 64.9 | 82.7 | 7,230 | 530 | 706 | 9.36 |
| 323.9 × 8.0 | 62.3 | 79.4 | 9,900 | 611 | 808 | 11.2 |
| 323.9 × 10.0 | 77.4 | 98.6 | 12,200 | 753 | 1,000 | 11.1 |
| 406.4 × 10.0 | 97.8 | 125 | 24,100 | 1,190 | 1,570 | 13.9 |
| 457.0 × 12.5 | 137 | 175 | 42,700 | 1,870 | 2,480 | 15.6 |
Section properties based on BS 4-2:2004 and BS EN 10210. I = second moment of area. Wel = elastic section modulus. Wpl = plastic section modulus. i = radius of gyration. All values for S275 or S355 steel (grade does not affect section geometry).
Steel grade selection for CHS in UK structural applications is governed primarily by the structural design requirements — yield strength, fracture toughness, and weldability — alongside cost and availability. The two most commonly specified grades for structural CHS in UK construction in 2026 are S275 and S355, both conforming to BS EN 10025-2 for hot-rolled structural steel and BS EN 10210 for hot-finished hollow sections.
| Property | S235 | S275 | S355 | S420 |
|---|---|---|---|---|
| Yield Strength (fy, t ≤ 16mm) | 235 N/mm² | 275 N/mm² | 355 N/mm² | 420 N/mm² |
| Ultimate Tensile Strength (fu) | 360–510 N/mm² | 410–560 N/mm² | 470–630 N/mm² | 520–680 N/mm² |
| Yield Strength Advantage vs S275 | –15% | Baseline | +29% | +53% |
| Typical Section Weight Saving vs S275 | — | — | ~20–25% | ~30–35% |
| Standard for Hollow Sections | BS EN 10219 | BS EN 10210/10219 | BS EN 10210/10219 | BS EN 10219 |
| Sub-Grade for Fracture Toughness | S235JR/J0/J2 | S275JR/J0/J2 | S355JR/J0/J2/K2 | S420MH |
| 2026 Price Premium vs S275 | –3–5% | Baseline | +8–15% | +20–30% |
| Weldability | Excellent | Excellent | Good (preheat may be required) | Moderate (preheat required) |
| Typical UK Application | Light structures, handrails | General structural use | Long spans, columns, trusses | Specialist high-strength |
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CHS steel pricing in the UK in 2026 is quoted per tonne of steel section, with the price varying by steel grade, wall thickness, surface finish, and order quantity. Prices have broadly stabilised in 2026 after the significant volatility of 2021–2023, with global steel supply normalisation and reduced energy costs moderating the sharp price increases of the post-pandemic period. Trade account pricing at steel stockholders and fabricators consistently undercuts retail list prices by 10–20% for regular purchasers.
| Product / Specification | 2026 Price per Tonne | Notes |
|---|---|---|
| CHS S275 — Black / Mill Finish | £950–£1,150/tonne | Standard grade, no protection |
| CHS S275 — Primer Painted | £1,020–£1,220/tonne | One coat shop primer — standard |
| CHS S355 — Black / Mill Finish | £1,050–£1,280/tonne | High strength — ~10% premium |
| CHS S355 — Primer Painted | £1,120–£1,350/tonne | Most common structural spec |
| CHS S275 — Hot-Dip Galvanised | £1,350–£1,650/tonne | Galv surcharge + steel cost |
| CHS 316L Stainless Steel | £3,800–£5,200/tonne | Premium material — marine / arch. |
| Cutting to length (per cut) | £3–£8 per cut | Depends on section size and quantity |
| End profiling / cope-cutting | £15–£45 per end | CNC profiling for welded joints |
| Shot blasting (Sa2.5) | £80–£150/tonne | Pre-painting blast standard |
| Delivery (per tonne) | £45–£95/tonne | Often free above min order weight |
| CHS Size | Mass (kg/m) | S275 Primer (£/m) | S355 Primer (£/m) | Galvanised S275 (£/m) |
|---|---|---|---|---|
| 48.3 × 3.2 | 3.56 kg/m | £3.90–£4.65 | £4.20–£5.05 | £5.10–£6.20 |
| 76.1 × 5.0 | 8.77 kg/m | £9.60–£11.50 | £10.40–£12.40 | £12.50–£15.40 |
| 114.3 × 5.0 | 13.5 kg/m | £14.80–£17.70 | £15.90–£19.10 | £19.30–£23.60 |
| 168.3 × 6.3 | 25.2 kg/m | £27.60–£33.00 | £29.70–£35.60 | £36.00–£44.00 |
| 168.3 × 10.0 | 38.7 kg/m | £42.40–£50.80 | £45.70–£54.60 | £55.30–£67.70 |
| 219.1 × 10.0 | 51.6 kg/m | £56.50–£67.60 | £60.90–£72.80 | £73.70–£90.30 |
| 273.0 × 10.0 | 64.9 kg/m | £71.10–£85.10 | £76.60–£91.50 | £92.60–£113.60 |
| 323.9 × 10.0 | 77.4 kg/m | £84.80–£101.50 | £91.40–£109.20 | £110.50–£135.50 |
| 406.4 × 10.0 | 97.8 kg/m | £107.20–£128.30 | £115.50–£137.80 | £139.60–£171.20 |
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Structural CHS steel requires appropriate corrosion protection for its intended exposure environment and design service life. The choice of surface finish significantly affects both the initial material cost and the whole-life maintenance cost of the steel structure — decisions made at the specification stage have direct implications for the building's long-term operational and maintenance budget. UK structural steel specifications for CHS typically follow the recommendations of BS EN ISO 12944 (corrosion protection of steel structures by protective paint systems) and the SCI Publication P347 (Architecturally Exposed Structural Steel).
CHS supplied in the as-rolled or as-formed mill finish condition — known as black steel — has a thin layer of mill scale on the surface that provides minimal corrosion protection. Black CHS is suitable only for internal dry environments where relative humidity remains consistently below approximately 60%, or for elements that will be encased in concrete or fire protection materials immediately after erection. For any external or moisture-exposed application, black CHS must be cleaned and coated before use. Shot blasting to Sa2.5 (near white) per BS EN ISO 8501-1 before painting is required for most structural coating specifications.
The most common surface finish for structural CHS in UK construction — a single coat of zinc phosphate or zinc-rich primer applied in the fabrication shop before delivery to site. Shop primer provides temporary corrosion protection during transport, storage, and erection, and a key surface for the subsequent full protective coating system applied on site. The primer system alone is not a complete corrosion protection solution — it must be followed by intermediate and finish coats in accordance with the project's ISO 12944 corrosion category specification before the structure is exposed to its service environment.
Hot-dip galvanised CHS provides excellent long-term corrosion protection for external and moderately aggressive environments through a metallurgically bonded zinc coating of typically 50–100 microns. Galvanised CHS is widely used in external canopies, car parks, agricultural buildings, coastal structures, and any application where a low-maintenance finish is required. The galvanising process involves immersing the fabricated steel in molten zinc at approximately 450°C — requiring clean steel and careful attention to drainage holes in hollow sections to prevent trapped zinc causing distortion or bursting. Always specify internal drainage holes in CHS members before galvanising to allow zinc to flow through and drain from hollow interiors.
Stainless steel CHS in Grade 316L (molybdenum-bearing, superior marine and chloride resistance) or Grade 304 (general purpose) is specified for the most demanding corrosion environments and for architecturally exposed applications where the natural lustre of polished or brushed stainless steel is an aesthetic requirement. Common UK applications include marine and offshore structures, food processing facilities, architectural balustrades and handrails, external cladding supports in coastal locations, and visible structural elements in high-quality commercial interiors. The material cost is approximately 3.5–4.5 times higher than structural carbon steel CHS of equivalent section — justified only where the combination of corrosion performance, aesthetic quality, and whole-life maintenance savings supports the premium.
| Finish | Corrosion Category (ISO 12944) | Expected Service Life | Maintenance Required | Best Application |
|---|---|---|---|---|
| Black / Mill Finish | C1 only (internal dry) | Short — no protection | Coat immediately | Concrete-encased, dry internal |
| Shop Primer Only | C2 (temporary) | 2–5 years (temporary) | Full system required on site | All sheltered internal structural |
| Full Paint System | C2–C5 dependent on system | 10–25+ years | Maintenance re-coat 10–20 years | Internal / external structural |
| Hot-Dip Galvanised | C3–C4 | 20–40+ years | Very low / inspect only | External, agricultural, car parks |
| Galv + Paint (duplex) | C4–C5 | 40–60+ years | Minimal | Aggressive external environments |
| 316L Stainless Steel | C5M / Im3 (marine) | 50–100+ years | Negligible (cleaning only) | Marine, coastal, food, architectural |
Structural CHS members in UK construction are designed to BS EN 1993-1-1 (Eurocode 3 — General Rules) and BS EN 1993-1-8 (Joints in Steel Structures), with the UK National Annex providing UK-specific parameters. Connection design for CHS-to-CHS welded joints follows BS EN 1993-1-8 Chapter 7 — the comprehensive set of design rules for welded CHS joints in trusses and lattice girders including K-joints, T-joints, X-joints, and N-joints.
CHS sections are classified as Class 1, 2, 3, or 4 depending on the D/t ratio (diameter-to-thickness ratio) relative to the steel yield strength. Class 1 and 2 sections can develop their plastic moment capacity — essential for plastic analysis and for connection design to Chapter 7 of BS EN 1993-1-8. The classification limits for CHS under bending and axial compression per Eurocode 3 are:
For S275 steel (ε = √(235/275) = 0.924): Class 1 limit D/t ≤ 42.7; Class 2 limit D/t ≤ 59.8. For S355 steel (ε = 0.814): Class 1 limit D/t ≤ 33.2; Class 2 limit D/t ≤ 46.4.
CHS columns are designed to BS EN 1993-1-1 using buckling curve 'a' for hot-finished CHS (BS EN 10210) and buckling curve 'c' for cold-formed CHS (BS EN 10219), reflecting the residual stress profile of each production method. The equal radius of gyration in all directions means that CHS columns buckle about any axis with equal ease, and the effective length used in compression design must account for the actual restraint conditions at both ends of the member. For a pin-ended column, effective length LE = L; for a fixed-both-ends column, LE = 0.5L.
Structural Steel Design Resources UK 2026: IStructE | Steel Construction Info (SCI) | BCSA | GOV.UK Approved Documents
CHS has identical section properties (I, Wel, Wpl, i) in every direction — the key structural advantage over I-sections and RHS/SHS. This makes CHS the most efficient section for multi-directional loading and columns with no preferred axis.
Structural CHS is manufactured to BS EN 10210 (hot-finished, better residual stress profile — buckling curve 'a') or BS EN 10219 (cold-formed, buckling curve 'c'). Specify the standard explicitly in structural steel drawings.
S275 is the standard structural steel grade for CHS in UK construction. Upgrade to S355 for long-span trusses, heavily loaded columns, or weight-critical structures — the 29% yield strength increase allows 20–25% section weight reduction.
All CHS weight calculations use steel density of 7,850 kg/m³. Mass per metre = cross-sectional area (mm²) × 7,850 / 10⁶. Published section tables in BS 4-2:2004 provide mass per metre for all standard UK CHS sizes.
CHS members must have adequate drainage holes drilled before hot-dip galvanising to allow molten zinc to flow through and drain from hollow interiors. Failure to provide drainage holes causes zinc trapping, pressure build-up, and potential bursting during galvanising.
CHS S275 primer-painted is typically priced at £1,020–£1,220 per tonne in the UK in 2026. S355 carries an 8–15% premium. Full price-per-metre rates depend on the section size (kg/m) — use the calculator above for accurate cost estimates.
Hot-finished CHS to BS EN 10210 uses buckling curve 'a' in Eurocode 3 column design — the most favourable buckling curve available, reflecting the lower residual stresses of the hot-finishing process vs cold-formed sections.
CHS section class is determined by the D/t ratio. Class 1 (plastic): D/t ≤ 50ε². Most standard structural CHS sections are Class 1 or 2, allowing full plastic moment capacity to be used in Eurocode 3 design.
Welded CHS joint design (K, T, X, N joints) is governed by BS EN 1993-1-8 Chapter 7. Joint efficiency depends on the diameter ratio β = d1/d0 and wall thickness ratio τ = t1/t0. Full-strength welds are required at all CHS-to-CHS connections.
CHS stands for Circular Hollow Section — a structural steel profile with a circular cross-section, characterised by its outside diameter (OD) and wall thickness (t). CHS is also commonly called steel tube, steel pipe, or round hollow section in UK construction. It is manufactured to BS EN 10210 (hot-finished) or BS EN 10219 (cold-formed) and is widely used for structural columns, trusses, bracing members, space frames, architectural exposed steelwork, handrails, and any application where circular geometry, equal stiffness in all directions, or aesthetic appeal is required.
CHS weight per metre = Cross-sectional area (m²) × Steel density (7,850 kg/m³). Cross-sectional area A = π/4 × (D² – d²), where D = outside diameter in mm and d = inside diameter = D – 2t (t = wall thickness). In mm²: A = π/4 × (D² – (D–2t)²). Convert to m²: divide by 10⁶. Multiply by 7,850 to get kg/m. Example: 168.3 × 10.0 CHS — D=168.3mm, d=148.3mm, A = π/4 × (168.3² – 148.3²) = π/4 × (28,325 – 21,993) = π/4 × 6,332 = 4,974 mm² = 49.74 cm². Weight = 49.74 × 7.85/1,000 = 3.90 kg/cm × 10 = 38.7 kg/m (approximately). Our calculator performs this calculation automatically.
CHS (Circular Hollow Section) has a round cross-section with equal properties in all directions. RHS (Rectangular Hollow Section) and SHS (Square Hollow Section) have flat faces and equal properties in two perpendicular axes only. CHS is preferred for columns under multi-directional loading, trusses with welded joints (easier CHS-to-CHS welding without gussets), and architecturally exposed elements where a circular profile is required. RHS/SHS is preferred for beams (higher section modulus about the major axis), bolted connections (flat face facilitates bolting), and situations where the flat face provides a simpler connection detail. RHS/SHS also stacks and stores more easily than CHS.
CHS S275 black (mill finish) is typically priced at £950–£1,150 per tonne in the UK in 2026. Primer-painted S275 CHS is £1,020–£1,220 per tonne. S355 primer-painted is £1,120–£1,350 per tonne. Hot-dip galvanised CHS is approximately £1,350–£1,650 per tonne including the galvanising charge. Stainless steel 316L CHS is £3,800–£5,200 per tonne. Trade account pricing at steel stockholders undercuts these rates by 10–20%. Cut-to-length charges of £3–£8 per cut apply for non-standard lengths. Delivery charges of £45–£95 per tonne apply unless minimum weight thresholds are met.
Standard UK CHS sizes range from 21.3mm OD (smallest) through to 508mm OD (and larger for specialist applications), with wall thicknesses from 2.6mm upwards. The most commonly stocked sizes at UK steel stockholders include: 48.3, 60.3, 76.1, 88.9, 114.3, 139.7, 168.3, 193.7, 219.1, 244.5, 273.0, 323.9, and 355.6mm OD with multiple wall thicknesses at each diameter. Full size ranges are listed in BS 4-2:2004 and in the BCSA/SCI Steelwork Design Guide (Blue Book) which is the standard UK reference for structural hollow section properties.
The elastic section modulus (Wel) of a CHS = I / (D/2), where I = π/64 × (D⁴ – d⁴) is the second moment of area and D/2 is the distance from the neutral axis to the outer fibre. For a 168.3 × 10.0 CHS: I = π/64 × (168.3⁴ – 148.3⁴) = 1,290 cm⁴ (from section tables). Wel = 1,290 / (168.3/20) = 1,290 / 8.415 = 153 cm³. The plastic section modulus Wpl = (D³ – d³) / 6, used for Class 1 and 2 sections in plastic analysis under Eurocode 3. These values are published in standard section tables and calculated automatically by our CHS calculator.
The radius of gyration (i) of a CHS = √(I/A), where I is the second moment of area and A is the cross-sectional area. For CHS, i is the same in all directions (unlike I-sections where ixx ≠ iyy), which is a key structural advantage. For a 168.3 × 10.0 CHS: I = 12,900,000 mm⁴ (1,290 cm⁴), A = 4,930 mm² (49.3 cm²), i = √(12,900,000 / 4,930) = √2,617 = 51.2 mm = 5.12 cm. The radius of gyration governs buckling resistance in compression — a higher i means lower slenderness and higher buckling resistance at the same effective length.
Use S275 as the default for standard structural CHS in UK construction where member sizes are not critical and the overall steel tonnage is modest. Specify S355 when the structural engineer's design shows that S275 would require a significantly larger CHS diameter or wall thickness to carry the design loads — typically for long-span trusses (spans over 12–15m), heavily loaded columns in multi-storey buildings, and weight-critical structures. S355 carries an 8–15% cost premium per tonne but allows approximately 20–25% reduction in section weight in strength-controlled designs, often producing a net cost saving while also reducing dead load on supporting elements. Always confirm grade with the structural engineer — specifying S355 where S275 suffices is unnecessary expenditure.
BS EN 10210 covers hot-finished structural hollow sections — CHS produced by hot-forming, which removes the residual stresses introduced during cold-forming and produces a more uniform cross-section. Hot-finished CHS uses buckling curve 'a' in Eurocode 3 column design — the most favourable available. BS EN 10219 covers cold-formed structural hollow sections — CHS produced by cold-rolling or draw-forming from flat plate or strip, which has higher residual stresses and uses buckling curve 'c' in Eurocode 3, giving lower calculated buckling resistance at the same D/t ratio. For structural column applications, hot-finished CHS to BS EN 10210 is generally preferred where buckling resistance is critical. Always specify the standard explicitly in structural steel drawings to avoid misunderstanding between supplier and fabricator.
For hot-dip galvanising of CHS, the following specification requirements must be addressed: (1) Material — ensure steel is suitable for galvanising (silicon content 0.03% or 0.15–0.25% for reactive steels per BS EN ISO 1461 recommendations); (2) Drainage holes — drill adequate venting and drainage holes at the ends and at intermediate points on longer members to allow zinc to enter, flow through, and drain from hollow interiors — failure to provide drainage holes causes trapped zinc, pressure buildup, and risk of section bursting; (3) Suspension points — specify suspension hole locations for the galvanising bath crane; (4) Coating thickness — minimum 45 microns average, 35 microns locally per BS EN ISO 1461; (5) Post-galvanising — inspect for runs, drips, and bare spots before delivery to site.
The external surface area of a CHS per metre length = π × D (in metres) × 1m = π × D m²/m. For 168.3mm CHS: π × 0.1683 = 0.529 m²/m. Internal surface area = π × d = π × (D – 2t). For most structural applications, only the external surface area is painted or coated — internal surfaces are typically left uncoated in dry internal environments, or sealed and filled with nitrogen or dry air in aggressive environments to prevent internal corrosion in sealed hollow sections. Our calculator provides the external surface area per total length to assist with paint and coating quantity estimation.
Yes — concrete-filled CHS columns (CFSC or CFST — Concrete-Filled Steel Tube) are an efficient and increasingly popular structural form in UK multi-storey construction. The steel tube acts as permanent formwork and as the structural steel section, while the concrete filling contributes additional compression capacity and substantially improves the fire resistance of the column without external intumescent coating (the concrete acts as a heat sink, keeping the steel below its critical temperature for considerably longer than an unfilled tube). Concrete-filled CHS columns are designed to BS EN 1994-1-1 (Eurocode 4 — Composite Structures). The concrete should be a self-compacting or highly workable mix (C30/37 or C35/45 with S4/S5 slump) to ensure the hollow section is fully filled without voids.
Additional UK Steel and Structural Resources 2026: Steel design at Steel Construction Info | BCSA at bcsa.org.uk | Structural engineering at IStructE | Materials at Builder Depot | Safety at HSE | Regulations at GOV.UK Approved Documents
© 2026 CHS Calculator UK. Section properties based on BS 4-2:2004, BS EN 10210, and BS EN 10219. Verify all structural design calculations with a qualified structural engineer. Steel prices are indicative — verify current rates with your steel supplier before ordering. This calculator is provided as an estimation tool only.