Complete RSJ Size Chart 2026: Dimensions, Weights, and Safe Loads for All Common Sections
Whether you’re a structural engineer specifying beams for a commercial project or a homeowner trying to understand what the builder has quoted, this comprehensive RSJ size chart gives you everything you need. Every commonly stocked rolled steel joist and Universal Beam section is listed here with its dimensions, mass per metre, second moment of area, and elastic section modulus — the four properties that govern beam performance.
Bookmark this page. It is updated annually and cross-referenced against current BS EN 10365:2017 dimensional tolerances and BS 5950 design guidance.
How to Read RSJ Designations
RSJ beams are designated using three numbers separated by × symbols:
Format: Depth × Width × Mass per metre
Example: 203 × 133 × 25
- 203 mm — Overall depth (height) of the beam, measured from top flange to bottom flange
- 133 mm — Flange width (the horizontal shelf at top and bottom)
- 25 kg/m — Mass per linear metre; multiply by length to get total weight
This designation system follows BS EN 10365 and is used universally by UK, Irish and European suppliers. However, be aware that older drawings may use imperial equivalents such as 8” × 5¼” × 25 lb/ft — an 8-inch deep beam of approximately 203 mm depth.
Why the Shape Matters
The I-section (or H-section for Universal Columns) concentrates material in the flanges, far from the neutral axis. This maximises the second moment of area (I) relative to the weight. A solid square bar of the same mass would deflect many times more under an equivalent load. This is why RSJ and Universal Beam sections are so efficient for spanning horizontal distances — you get structural performance without excessive self-weight.
Understanding the Key Properties: I and Z
Before diving into the tables, it helps to understand what I_x and Z_x actually mean in practice.
I_x — Second Moment of Area (cm⁴)
This is a geometric property measuring how the cross-section resists bending. A larger I means less deflection under the same load. Deflection under a uniformly distributed load is calculated as:
δ = (5 × w × L⁴) / (384 × E × I)
Where:
- δ = maximum deflection (mm)
- w = load per unit length (kN/m)
- L = span (mm)
- E = 210,000 N/mm² for steel
- I = second moment of area (mm⁴)
Z_x — Elastic Section Modulus (cm³)
Z_x determines the maximum bending stress in the outer fibres of the beam. A larger Z means the beam can carry more moment before yielding. The allowable moment capacity (simplified for S275 steel) is:
M_allowable ≈ Z_x × 165 N/mm² (with typical safety factors applied)
For S355 steel, use 210 N/mm² as the allowable stress in preliminary calculations.
Complete RSJ/UB Size Chart
Small Sections (127–178 mm depth)
These lighter sections suit narrow openings such as single door widths, small window lintels, or secondary beams spanning short distances. They are easiest to handle — two or three people can often manage without mechanical lifting — but their load capacity is limited.
| Designation | Depth (mm) | Width (mm) | Web Thick (mm) | Flange Thick (mm) | Weight (kg/m) | I_x (cm⁴) | Z_x (cm³) |
|---|---|---|---|---|---|---|---|
| 127×76×13 | 127 | 76 | 4.0 | 7.6 | 13.0 | 473 | 83 |
| 152×89×16 | 152 | 89 | 4.5 | 7.7 | 16.0 | 869 | 119 |
| 152×127×37 | 152 | 127 | 6.4 | 10.7 | 37.0 | 1,358 | 159 |
| 178×102×19 | 178 | 102 | 4.8 | 7.9 | 19.0 | 1,357 | 146 |
| 178×127×26 | 178 | 127 | 5.8 | 10.2 | 26.0 | 1,690 | 194 |
Safe Working Load Examples (simply supported, uniformly distributed):
- 152×127×37 at 2.5 m span: approximately 10 kN/m
- 178×102×19 at 3.0 m span: approximately 5 kN/m
- 178×127×26 at 2.5 m span: approximately 8 kN/m
Typical applications: Single-door knockthroughs, garage door lintels, short-span secondary beams in timber floor systems, chimney breast removal above ground level.
Medium Sections (203 mm depth)
The 203 mm family — especially the 203×133×25 — is the workhorse of domestic construction in the UK. Structural engineers specify it for the vast majority of standard wall knockthroughs in two-storey terraced and semi-detached houses. It sits comfortably on standard 215 mm padstones and fits within a standard timber stud cavity.
| Designation | Depth (mm) | Width (mm) | Web Thick (mm) | Flange Thick (mm) | Weight (kg/m) | I_x (cm⁴) | Z_x (cm³) |
|---|---|---|---|---|---|---|---|
| 203×102×23 | 203 | 102 | 5.4 | 9.3 | 23.0 | 2,107 | 197 |
| 203×133×25 | 203 | 133 | 5.7 | 7.8 | 25.0 | 2,896 | 208 |
| 203×133×30 | 203 | 133 | 6.4 | 9.6 | 30.0 | 3,438 | 245 |
| 203×203×46 | 203 | 203 | 7.2 | 11.0 | 46.0 | 4,568 | 410 |
| 203×203×52 | 203 | 203 | 7.9 | 12.5 | 52.0 | 5,261 | 472 |
Safe Working Load Examples:
- 203×133×25 at 3.0 m span: approximately 8.5 kN/m
- 203×133×25 at 3.5 m span: approximately 6.5 kN/m
- 203×133×30 at 4.0 m span: approximately 6.0 kN/m
- 203×203×52 at 4.0 m span: approximately 12 kN/m
Real-world note: A 203×133×25 at 3 m with 3 kN/m load will deflect roughly 1.8 mm. At 3.5 m the same load causes 3.5 mm — well within the span/360 limit of 9.7 mm. This is why engineers rarely upgrade from ×25 to ×30 unless point loads are present or the span exceeds 4 m under typical house loads.
Typical applications: Open-plan kitchen/dining conversions, load-bearing wall removal between living and dining room, ground-floor rear extensions, garage conversions requiring header beams.
Large Sections (254 mm depth)
The 254 mm family begins where the 203 mm sections start to struggle — longer spans, heavier floor loads from bathrooms, or situations where two floors bear onto the beam. They are noticeably heavier and typically require three to four people or a powered chain block for installation.
| Designation | Depth (mm) | Width (mm) | Web Thick (mm) | Flange Thick (mm) | Weight (kg/m) | I_x (cm⁴) | Z_x (cm³) |
|---|---|---|---|---|---|---|---|
| 254×102×22 | 254 | 102 | 5.7 | 6.8 | 22.0 | 2,842 | 215 |
| 254×102×25 | 254 | 102 | 6.0 | 8.4 | 25.0 | 3,292 | 248 |
| 254×102×28 | 254 | 102 | 6.3 | 10.0 | 28.0 | 3,716 | 279 |
| 254×146×31 | 254 | 146 | 6.0 | 8.6 | 31.0 | 6,572 | 354 |
| 254×146×37 | 254 | 146 | 6.3 | 10.9 | 37.0 | 7,628 | 411 |
| 254×146×43 | 254 | 146 | 7.2 | 12.7 | 43.0 | 8,503 | 464 |
| 254×254×73 | 254 | 254 | 8.6 | 14.2 | 73.0 | 11,313 | 777 |
| 254×254×89 | 254 | 254 | 10.3 | 17.3 | 89.0 | 13,640 | 950 |
Safe Working Load Examples:
- 254×146×31 at 4.5 m span: approximately 7.0 kN/m
- 254×146×31 at 5.0 m span: approximately 5.5 kN/m
- 254×146×37 at 5.5 m span: approximately 5.4 kN/m
- 254×254×89 at 5.0 m span: approximately 20 kN/m
Note on the narrow-flange 254×102 series: Despite their 254 mm depth, the 102 mm flange width limits their resistance to lateral torsional buckling. For unrestrained spans, engineers often prefer the 254×146 series even at slightly lower loads, because the wider flange dramatically improves stability under real-world construction conditions.
Typical applications: Loft conversion ridge beams, rear extensions supporting first-floor loads, garage conversions where a car and rooms above combine, spans over 4 m in heavier-duty residential situations.
Extra Large Sections (305 mm+ depth)
These sections enter semi-commercial territory. While occasionally used in ambitious domestic projects — particularly loft conversions in Victorian terrace houses with long rear additions — they are most common in commercial fit-outs, industrial mezzanines, and multi-storey residential construction.
| Designation | Depth (mm) | Width (mm) | Web Thick (mm) | Flange Thick (mm) | Weight (kg/m) | I_x (cm⁴) | Z_x (cm³) |
|---|---|---|---|---|---|---|---|
| 305×102×25 | 305 | 102 | 5.8 | 6.8 | 25.0 | 4,392 | 265 |
| 305×102×28 | 305 | 102 | 6.0 | 8.8 | 28.0 | 5,180 | 311 |
| 305×102×33 | 305 | 102 | 6.6 | 10.8 | 33.0 | 6,070 | 364 |
| 305×165×40 | 305 | 165 | 6.0 | 10.2 | 40.0 | 12,350 | 568 |
| 305×165×46 | 305 | 165 | 6.7 | 11.8 | 46.0 | 14,100 | 652 |
| 305×165×54 | 305 | 165 | 7.9 | 13.7 | 54.0 | 16,100 | 749 |
| 305×305×97 | 305 | 305 | 9.9 | 15.4 | 97.0 | 26,390 | 1,472 |
| 305×305×118 | 305 | 305 | 12.0 | 18.7 | 118.0 | 31,930 | 1,784 |
Safe Working Load Examples:
- 305×165×40 at 6.0 m span: approximately 6.3 kN/m
- 305×165×46 at 6.5 m span: approximately 6.0 kN/m
- 305×165×54 at 7.0 m span: approximately 5.5 kN/m
- 305×305×118 at 7.0 m span: approximately 17 kN/m
Typical applications: Spans over 6 m in domestic concealed ridge beams, commercial retail ceiling voids requiring long clear spans, mezzanine floor edges, and primary beams carrying secondary beams.
Very Large Sections (356–457 mm depth)
Heavy commercial and industrial sections. Residential use is very rare, except occasionally in substantial steel-framed house construction or barn conversions.
| Designation | Depth (mm) | Width (mm) | Web Thick (mm) | Flange Thick (mm) | Weight (kg/m) | I_x (cm⁴) | Z_x (cm³) |
|---|---|---|---|---|---|---|---|
| 356×171×45 | 356 | 171 | 6.9 | 9.7 | 45.0 | 17,100 | 764 |
| 356×171×51 | 356 | 171 | 7.4 | 11.5 | 51.0 | 19,610 | 876 |
| 356×171×57 | 356 | 171 | 8.1 | 13.0 | 57.0 | 21,880 | 979 |
| 356×171×67 | 356 | 171 | 9.1 | 15.7 | 67.0 | 25,400 | 1,142 |
| 406×178×54 | 406 | 178 | 7.7 | 10.9 | 54.0 | 24,380 | 987 |
| 406×178×60 | 406 | 178 | 7.9 | 12.8 | 60.0 | 27,690 | 1,122 |
| 406×178×67 | 406 | 178 | 8.8 | 14.3 | 67.0 | 30,580 | 1,244 |
| 406×178×74 | 406 | 178 | 9.5 | 16.0 | 74.0 | 33,570 | 1,367 |
| 457×191×67 | 457 | 191 | 8.5 | 12.7 | 67.0 | 35,110 | 1,266 |
| 457×191×74 | 457 | 191 | 9.0 | 14.5 | 74.0 | 39,360 | 1,424 |
| 457×191×82 | 457 | 191 | 9.9 | 16.0 | 82.0 | 43,270 | 1,570 |
| 457×191×89 | 457 | 191 | 10.5 | 17.7 | 89.0 | 47,170 | 1,715 |
Note: For this size range, always engage a structural engineer and consider crane or HIAB access for delivery and installation. These beams weigh 250–500 kg for a typical 5–6 m length.
How to Use These Tables for Beam Selection
Step 1 — Determine Required Section Modulus (Z_x)
First, you need to calculate the maximum bending moment (M) your beam must resist.
For a simply supported beam with uniformly distributed load (UDL):
- M = (w × L²) / 8
Where:
- w = total distributed load in kN/m (dead + live)
- L = span in metres
Then, find the required section modulus:
- Z_required = M × 1,000 / σ_allowable
Where:
- σ_allowable = 165 N/mm² for S275 steel (with partial safety factors)
Worked example: Load = 8 kN/m, Span = 4.0 m M = (8 × 4²) / 8 = 16 kNm Z_required = 16,000 / 165 = 97 cm³
Scanning the table: 152×127×37 (Z = 159 cm³) would pass the strength check. But check deflection before finalising.
Step 2 — Check Deflection
Use: δ = (5 × w × L⁴) / (384 × E × I)
For our worked example:
- w = 8 kN/m = 8 N/mm
- L = 4,000 mm
- E = 210,000 N/mm²
- I for 152×127×37 = 1,358 cm⁴ = 13,580,000 mm⁴
δ = (5 × 8 × 4000⁴) / (384 × 210,000 × 13,580,000) = 12.6 mm
Allowable deflection at span/360 = 4000/360 = 11.1 mm
The 152×127×37 fails on deflection — only just, but it fails. The next step up is the 178×127×26 with I = 1,690 cm⁴:
δ = (5 × 8 × 4000⁴) / (384 × 210,000 × 16,900,000) = 10.1 mm ✓
This illustrates an important lesson: the deflection check, not the bending strength check, often governs beam selection, particularly for longer spans with moderate loads.
Step 3 — Select the Most Economical Section
Usually you want the lightest (cheapest) beam that satisfies both checks. However, also consider:
- Is the beam readily available from your local supplier? (Stock-holding varies by region)
- Does the beam depth fit within the available structural zone?
- Does the flange width provide adequate bearing on your padstones?
European IPE Sections — Quick Comparison
If you are working from European supplier catalogues (common in Ireland and throughout continental Europe), IPE sections are not identical to UK RSJ or UB sections but are closely compatible.
| IPE Size | Closest UK Equiv | Depth (mm) | Width (mm) | Weight (kg/m) | I_x (cm⁴) |
|---|---|---|---|---|---|
| IPE 140 | 152×127×37 | 140 | 73 | 12.9 | 541 |
| IPE 160 | 152×89×16 | 160 | 82 | 15.8 | 869 |
| IPE 180 | 178×102×19 | 180 | 91 | 18.8 | 1,317 |
| IPE 200 | 203×133×25 | 200 | 100 | 22.4 | 1,943 |
| IPE 220 | 203×133×30 | 220 | 110 | 26.2 | 2,772 |
| IPE 240 | 254×102×22 | 240 | 120 | 30.7 | 3,892 |
| IPE 270 | 254×146×31 | 270 | 135 | 36.1 | 5,790 |
| IPE 300 | 305×165×40 | 300 | 150 | 42.2 | 8,356 |
| IPE 330 | 305×165×46 | 330 | 160 | 49.1 | 11,770 |
| IPE 360 | 356×171×51 | 360 | 170 | 57.1 | 16,270 |
Critical warning: IPE sections are not direct substitutes for UK sections of a similar depth. The flange widths and thicknesses differ, so I and Z values are different. Always check the properties of the specific section you are ordering against what the structural engineer has specified. Never swap a 203×133×25 for an IPE 200 without engineering sign-off.
Weight per Length — Quick Reference for Handling and Delivery
Understanding beam weights before delivery day saves a lot of headaches. A 6-metre 254×146×37 weighs 222 kg — several times the safe single-person manual handling limit of 25 kg.
| Beam Size | 3 m | 4 m | 5 m | 6 m | Transport note |
|---|---|---|---|---|---|
| 127×76×13 | 39 kg | 52 kg | 65 kg | 78 kg | Two people adequate |
| 152×127×37 | 111 kg | 148 kg | 185 kg | 222 kg | Engine lift/chain block |
| 203×133×25 | 75 kg | 100 kg | 125 kg | 150 kg | 3 people or chain block |
| 203×133×30 | 90 kg | 120 kg | 150 kg | 180 kg | Chain block recommended |
| 254×146×31 | 93 kg | 124 kg | 155 kg | 186 kg | Chain block essential |
| 254×146×37 | 111 kg | 148 kg | 185 kg | 222 kg | Chain block/crane |
| 305×165×40 | 120 kg | 160 kg | 200 kg | 240 kg | Crane or engine hoist |
| 305×165×54 | 162 kg | 216 kg | 270 kg | 324 kg | Crane essential |
Safe handling summary:
- Under 50 kg: One or two people with correct technique
- 50–100 kg: 2–3 people; assess site conditions
- 100–200 kg: 3–4 people OR a chain block/engine lift
- Over 200 kg: Always use mechanical lifting equipment
Plan your access route before delivery. A 6 m beam cannot be manoeuvred around a 90° bend in a narrow hallway. Many installers use a Tirfor winch or engine hoist positioned in the opening itself to raise the beam to bearing height.
Steel Grades — What Matters in Practice
Most RSJ and UB beams are stocked in S275 steel. S355 is available on order from larger stockholders and at a modest premium. Here is a practical comparison:
| Property | S275 | S355 | S450/S460 |
|---|---|---|---|
| Yield strength | 275 N/mm² | 355 N/mm² | 450–460 N/mm² |
| Typical premium over S275 | — | +5–10% cost | +15–25% cost |
| Common UK availability | Excellent — standard stock | Good — usually to order | Limited |
| Suitable for | All residential, most commercial | Heavy commercial, longer spans | Specialist/industrial |
In practice, for domestic RSJ installations, you are almost always working with S275. Requesting S355 is worthwhile when a structural engineer has specified it — it allows the use of a slightly smaller, lighter beam section — but it adds complexity to the supply chain and small orders may take longer to arrive.
Frequently Asked Questions
Q: All the tables show I_x and Z_x — what about Z_y for the minor axis?
For beams loaded vertically (the standard case), you need I_x and Z_x — the major axis values. I_y and Z_y relate to horizontal loading (wind on the web face, for example) which is rarely the governing case for building beams. The tables above cover the properties needed for vertical load design.
Q: My old drawings show an 8” × 5¼” RSJ. What is the modern equivalent?
An 8-inch RSJ is approximately a 203 mm deep section. The 5¼-inch (133 mm) flange width points to the 203×133 family. The closest section is 203×133×25 or 203×133×30. Ask your structural engineer to confirm before ordering.
Q: Can I cut an RSJ on site with an angle grinder?
Cutting is possible with a 230 mm angle grinder and cutting disc, but it is slow, produces sparks, and results in rough cut faces that need grinding smooth before bearing. A cold saw or mitre saw with a metal cutting blade is faster and more accurate. For critical bearing surfaces, have the beam cut to length by the supplier on their saw bench — it’s usually only £10–30 per cut and gives a clean, square face.
Q: What is the difference between RSJ and UB sections?
Older RSJ sections had tapered inner flange faces (slope 1:6). Modern Universal Beams (UB) have parallel flanges and are produced to tighter tolerances. In practice, the terms are used interchangeably in domestic construction, but for bolted connections where flange parallelism matters — standard bolted joints, moment connections — Universal Beams are preferred. The safe load tables for RSJ sections are based on UB properties for consistency.
Q: I need to span 7 metres. Is that achievable with a standard section?
Yes — but you will be into the 356 mm or 406 mm depth sections depending on the load. A 356×171×67 at 7 m carrying 5 kN/m (equivalent to a bedroom floor above with light partitions) gives a deflection of approximately 14.6 mm — within the span/360 limit of 19.4 mm. However, a 7 m beam in domestic construction often cannot be delivered without a HIAB lorry, and installation requires a chain hoist or engine lift at minimum. Budget for crane hire if the site is constrained.
Material Grades — Technical Notes
S275 steel is by far the most commonly held section steel in UK stockholders. It meets BS EN 10025-2:2019. Yield strength is 275 N/mm² for section thicknesses up to 16 mm, reducing to 265 N/mm² for thicknesses between 16 and 40 mm — a minor point, but one that engineers account for in calculations for the thicker-flanged heavy sections.
S355 steel operates with a yield strength of 355 N/mm² (up to 16 mm thickness) and 345 N/mm² between 16–40 mm. This 29% increase in strength means the engineer can specify a section approximately one size lighter than equivalent S275, saving perhaps £5–15 per metre in material cost. However, procurement on small orders can add weeks of lead time, so confirm availability with your supplier first.
CE Marking: All structural steel sections sold in the UK must carry CE or UKCA marking confirming compliance with BS EN 10025. Always request a mill test certificate from your supplier, confirming the heat number, grade, and chemical composition. This is essential if the structural engineer requires documented evidence of material quality.
Conclusion
This reference chart covers the full range of RSJ and Universal Beam sections available from UK stockholders in 2026. Use the I_x values for deflection checks and Z_x values for bending strength. The worked examples demonstrate that deflection, rather than stress, typically governs beam selection for residential floor spans.
Key takeaways:
- The 203×133×25 is the standard domestic knockthrough beam for spans up to 4 m at typical house loads
- Always run both a strength check (Z_x) and a deflection check (I_x) before finalising a section
- IPE sections and UK UB sections are similar but not interchangeable — verify properties against the specific section used
- Handling becomes a crane or hoist job for any beam over 150 kg total weight
- Always purchase to the steel grade specified by your structural engineer and request a mill certificate
Always have final beam selection verified by a chartered structural engineer before purchase and installation. These tables provide guidance for preliminary design only.
Disclaimer: All section properties are taken from manufacturers’ standard tables and are subject to manufacturing tolerances under BS EN 10365. Safe working loads are indicative only, based on S275 simply-supported beams with standard safety factors. Final specification must be produced by a qualified structural engineer.
