RHS and SHS — What They Are

Rectangular Hollow Section (RHS) and Square Hollow Section (SHS) are structural steel profiles with a hollow rectangular or square cross-section. They are widely used in construction, machinery, trailers, furniture, and general fabrication because they offer good strength-to-weight ratio and a clean, symmetrical appearance. SHS is simply a special case of RHS where width equals depth.

The Weight Formula — Without Corner Radius

For a simplified calculation ignoring corner radii (acceptable for quick estimates):

Weight (kg/m) = [(2 × (D + W) × T) − (4 × T²)] × 7.85 × 10⁻⁶ × 1000

Where D = depth (mm), W = width (mm), T = wall thickness (mm).

Simplified: Weight (kg/m) = [2 × (D + W) × T − 4T²] × 0.00785

Standard RHS Weight Table — Mild Steel

Standard SHS Weight Table — Mild Steel

Corner Radius Effect on Weight

Real RHS/SHS sections have rounded corners — the steel at the outside corners is removed compared to a sharp-corner model, and additional material fills the inside radius area. The net effect of corner radii is a slight reduction in cross-sectional area compared to the idealised sharp-corner formula. For typical structural sections, corner radii reduce weight by 1.5–3%.

For precise weight calculation matching published section properties, use our RHS/SHS Weight Calculator with Corner Radius, which implements the exact geometric formula accounting for inside and outside radii.

Worked Examples

Example 1 — SHS Column Length

100×100×5 mm SHS, 4 columns each 3.6 m long:

kg/m = 14.33 (from table)
Total = 14.33 × 3.6 m × 4 = 206.4 kg

Example 2 — RHS Beam

200×100×5 mm RHS, beam span 8 m:

Weight = 23.07 kg/m × 8 m = 184.6 kg

Example 3 — Gate Frame

Gate frame: 4 lengths of 75×50×3 mm RHS, each 2.4 m:

Weight = 5.19 kg/m × 2.4 m × 4 = 49.8 kg

RHS vs SHS — When to Use Which

RHS/SHS vs Other Structural Profiles — Comparison

RHS and SHS compete with several other structural steel profiles for most applications. Understanding the trade-offs helps in profile selection:

Designing with RHS — Practical Guidance

When designing structures using RHS or SHS, the following practical rules help ensure structurally efficient and fabrication-friendly designs:

Wall Thickness Selection

For most structural applications, the wall thickness should be at least 1/30 of the section width. Very thin-walled sections (wall-to-width ratio below 1/50) are prone to local buckling before the full section strength is developed. Common structural RHS designs use wall thicknesses of 3–6 mm for most light to medium applications and 6–12.5 mm for heavy structural use.

Connection Design

One significant advantage of RHS/SHS over open sections is the ease of end-plate connections. A flat end plate welded to the end of an RHS creates a clean bolted connection point — much easier to detail than an I-beam end connection. The hollow section also simplifies cleaning and painting — no internal faces to protect if the ends are sealed by end plates.

Fire Protection

Hollow sections require fire protection in buildings (as does all structural steel). The protected perimeter of an RHS is smaller than the perimeter of an equivalent I-beam of similar section modulus, which can make fire protection more economical — less intumescent paint or board protection surface area to cover.

Weight Optimisation — Choosing the Right Section

For a given load requirement, multiple RHS/SHS sections may technically work. The lightest (and usually cheapest) section that meets the structural requirement is the most economical choice. For columns, larger sections with thinner walls generally perform better than smaller sections with thick walls (better radius of gyration). For beams, deeper sections are more efficient than stocky ones.

Use our RHS Weight Calculator to quickly compare the weight of different sections for the same length, and our Cost Estimator to convert weight to cost at current steel prices.

Aluminium RHS and SHS — Lighter Alternative

Aluminium RHS and SHS sections are used extensively in applications where weight reduction is important — marine, transport, architectural, and aerospace structures. The weight calculation uses exactly the same formula as steel RHS/SHS, but with aluminium’s density (approximately 2,700 kg/m³ for 6061, the most common structural aluminium alloy) instead of steel’s 7,850 kg/m³. This means aluminium sections are approximately 2.9 times lighter than equivalent steel sections of the same dimensions.

However, aluminium’s elastic modulus (Young’s modulus) is also approximately one-third that of steel (70 GPa vs 200 GPa). This means that an aluminium section deflects approximately three times as much as a steel section of the same dimensions under the same load — a significant factor in beams and long spans. To match steel’s stiffness, aluminium sections need to be deeper, which partially offsets the weight advantage. The net result is that aluminium structures are typically 40–60% lighter than equivalent steel structures (not the theoretical 66% that pure density comparison suggests) because the sections must be increased in size to compensate for lower stiffness.

Weight calculation for aluminium RHS using the steel formula: simply substitute 2.7 for the density factor instead of 7.85. All other formula elements remain the same. A 100×50×4 mm aluminium RHS weighs approximately: [2×(100+50)×4 – 4×16] × 0.0027 = [1200 – 64] × 0.0027 = 1136 × 0.0027 = 3.07 kg/m, compared to 8.31 kg/m for the same section in mild steel — 63% lighter.

Cost Comparison — Steel vs Aluminium RHS

Aluminium RHS is typically 3–5 times more expensive per kg than mild steel RHS in most markets. Combined with the weight saving of approximately 65% for the same section dimensions (or 40–50% when aluminium sections are upsized for equivalent stiffness), the total cost premium for an all-aluminium structure vs all-steel is typically 100–200%. This premium is justified when weight savings translate into fuel savings (marine, transport), reduced foundation loads, ease of manual handling, or corrosion resistance that eliminates painting and maintenance costs over the structure’s lifetime.

Accuracy, Tolerances and Real-World Considerations

Every weight and dimension calculation in sheet metal work is an estimate until the material is measured. Understanding the gap between theoretical calculations and real-world results is what separates experienced fabricators from novices. Theoretical calculations give the exact answer for an ideal, perfectly manufactured piece of material with exactly the nominal dimensions. Real material departs from this ideal in several important ways.

First, mill thickness tolerances allow the supplied material to be within a band around the nominal value — typically ±10% for thinner gauges. A sheet nominally 2 mm thick may legitimately be anywhere from 1.8 mm to 2.2 mm and still meet the specification. Second, width and length tolerances allow the sheet to be slightly undersized or oversized — usually ±3–5 mm for standard mill sizes. Third, flatness tolerances allow some bow and camber that may require flattening before precision fabrication. Fourth, the actual density of the supplied material may vary slightly from the nominal value used in calculations, though this is typically less than 0.5% and negligible for most purposes.

The practical implication is that material quantities should always be ordered with margin — typically 5–10% over the calculated net requirement for simple rectangular parts, and 10–20% for complex profiles with significant scrap. Weight estimates should be understood as nominal values with a real-world range of approximately ±5% for procurement planning purposes.

For applications where exact weight matters — certified lifting equipment, vessel pressure calculations, precise logistics planning — measure the actual delivered material rather than relying on nominal calculations. A calibrated weighbridge or individual piece weighing with a certified scale provides the ground truth that nominal calculations cannot replace.

Sustainability and Weight Reduction

Accurate weight calculation is increasingly important for sustainability reporting and embodied carbon assessment. Steel production is energy-intensive, with approximately 1.8–2.2 tonnes of CO₂ emitted per tonne of steel produced (the exact value varies significantly by production method — electric arc furnace steel from recycled scrap emits approximately 0.4–0.6 tonnes CO₂/tonne, while blast furnace steel from iron ore emits approximately 2.0–2.5 tonnes CO₂/tonne). Minimising the mass of steel used in a project directly reduces its embodied carbon.

Weight calculation provides the foundation for embodied carbon assessment: total steel weight by grade and type, combined with emission factors from published databases (CIBSE TM65, ICE Database, EPD data), gives a credible project embodied carbon estimate. As sustainability requirements in construction become more stringent — through codes, client requirements, and green building rating systems — this kind of materials accounting becomes a routine part of project documentation. Fabricators who can provide accurate, auditable weight calculations by material type are better positioned to support this documentation for their clients.

Explore our complete range of calculators at sheetgauge.com — covering sheet weight, structural section weight, cost estimation, gauge conversion, and more — all free, all accurate, and all designed to support both quick estimates and detailed project calculations.

The calculations, tables, and guidance in this guide reflect established engineering practice in the steel fabrication industry. Whether you are a structural engineer sizing members for a commercial building, a procurement officer ordering material for an industrial project, a fabricator quoting a job, or a student learning the fundamentals of structural steel, the principles here provide a solid foundation. Accuracy in weight calculation translates directly into accuracy in cost estimation, transport planning, structural design, and sustainability accounting — it is one of the most broadly useful skills in engineering and construction practice. Use our calculators to apply these principles efficiently, and refer to the tables and formulas here whenever you need to verify or understand a result.