Indicative triage, not a design tool
Steel beam calculator: what size UK beam do you need?
Answer two questions, the span and what the beam carries, and we'll show the section range typically specified on UK domestic jobs like yours: openings to about 3 m with a floor above usually land between 152x152 UC23 and 203x203 UC46. Then get the real answer. Beam sizing is a structural engineer's calculation, and building control will want to see it.
Question 1
What is the clear span of the opening, in metres?
Measure the structural opening. The beam itself will be longer, because it has to bear on masonry at each end; how much bearing, and on what padstone, comes out of the calcs rather than a rule of thumb. Between sizes? Round up.
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Scope of this checker
- Openings in load-bearing walls: doors, knock-throughs, bifold openings
- Chimney breast removals and floor-plus-roof loads over an opening
- Spans from under 1 m to 6 m, and a straight answer above 6 m
- Indicative UC/UB section ranges only, drawn from typical UK domestic practice
- Every route ends the same way: a structural engineer's calculation to BS EN 1993, which is how Part A compliance is normally demonstrated to building control
Steel Beam Checker is an independent information site operated by Ellul Solutions Ltd. It is not affiliated with any engineering institution, steel supplier or building control body. Nothing on this site is structural engineering advice and no output here is a beam specification: sizing is a structural engineer's calculation under BS EN 1993 and the Building Regulations, and building control requires those calculations. Never order steel from this checker.
Get a structural engineer's calcs
Tell us about the opening and we'll introduce you to a structural engineer who handles domestic beam calcs for jobs like yours.
Indicative steel section ranges on UK domestic jobs
Last updated
The span and load bands the checker uses, with the UC/UB ranges typically specified on comparable UK domestic jobs. This is observed practice, not a span table: every row still needs an engineer's calculation.
Bands assembled from published UK domestic structural examples and steel supplier guidance, with section names checked against the SCI Blue Book listings. They describe what is commonly specified, not what your job needs: beam sizing depends on measured loads, deflection limits, bearing and restraint, and is a structural engineer's calculation under BS EN 1993. Building control requires those calculations, so never order steel from this table.
| Clear span | Supporting | Sections typically specified | What usually governs |
|---|---|---|---|
| Up to 3 m | Domestic floor only | 152x152 UC23 to 203x203 UC46 | Strength and simple bearing |
| Up to 3 m | Floor plus roof, or masonry | 203x203 UC46 and up, sometimes paired | Load path and padstone design |
| 3 to 4.5 m | Domestic floor only | 203x203 UC46 to 254x146 UB37 | Deflection starts to matter |
| 3 to 4.5 m | Floor plus roof, or masonry | 254 to 305 series UB, or heavy UC | Deflection and headroom |
| 4.5 to 6 m | Domestic floor only | 254x146 UB37 to 305x165 UB46 | Deflection |
| 4.5 to 6 m | Floor plus roof, or masonry | 305 to 356 series UB, sometimes paired or a frame | Deflection, restraint, connections |
| Over 6 m | Anything | No indicative range offered | Engineered design throughout |
- UK openings up to about 3 m with a domestic floor above typically see 152x152 UC23 to 203x203 UC46 specified, but the exact section is always a structural engineer's calculation.
- A structural engineer's calcs for a single domestic beam typically cost £250–£500 in 2026, against £1,600–£3,200 for the whole beam job installed.
- There is no deemed-to-satisfy span table for structural steel in domestic alterations: compliance with Part A is demonstrated by calculation to BS EN 1993, and the building control body decides what evidence satisfies it.
Cite this page
“Indicative steel section ranges on UK domestic jobs”, Steel Beam Checker, https://steelbeamchecker.co.uk/ (updated 2026-08-14). Bands assembled from published UK domestic structural examples and steel supplier guidance, with section names checked against the SCI Blue Book listings. They describe what is commonly specified, not what your job needs: beam sizing depends on measured loads, deflection limits, bearing and restraint, and is a structural engineer's calculation under BS EN 1993. Building control requires those calculations, so never order steel from this table.
Go deeper
Sourced, dated, kept current.
How much does an RSJ cost? Steel, calcs and fitting (2026)
Typical 2026 UK prices: a small domestic RSJ is £150–£300 supplied, engineer's calcs £250–£500, and a typical installed wall opening lands at £1,600–£3,200 all in.
What size RSJ do I need? The honest answer, span by span
Why there is no lookup answer for RSJ size: loads, deflection, bearing and padstones decide it. What engineers typically specify per span, and how to get real calcs.
Steel beam calculations for building control: what is required
Building control needs structural calculations before it signs off a beam: what the calcs must show, full plans vs building notice, typical fees and the completion cert.
Frequently asked
What size RSJ do I need for a 3m span?
On comparable UK jobs with only a domestic floor above, engineers typically specify between 152x152 UC23 and 203x203 UC46 over spans up to about 3 m. That is an observation from typical practice, not a design: your beam must be calculated by a structural engineer, and building control will ask for the calcs.
What size RSJ do I need for a 5m span, or a 4m one?
Floor-only spans of 3–4.5 m typically land between 203x203 UC46 and 254x146 UB37, and 4.5–6 m spans in the 254 to 305 series UBs, deeper again with roof or masonry above. Indicative only: deflection usually governs at these spans and only calculation settles it.
How much do steel beam calculations cost?
Typically £250–£500 in 2026 for a single domestic beam from a structural engineer, more for multiple beams or complex load paths. The installed beam job typically runs £1,600–£3,200 all in, so the calcs are the smallest line and the only legally load-bearing one.
Can I use a free steel beam calculator instead of an engineer?
Not for approval. Building control requires calculations from a competent person who takes professional responsibility for them, an anonymous web calculation, a span table or this checker's output does not qualify. Online tools, ours included, are for orientation before the engineer, not instead of one.
What is the difference between a UC and a UB?
Both are I-shaped steel sections. UCs (universal columns) are squarer and shallower, so they hide in floor zones and 215 mm walls, which is why they dominate small domestic openings. UBs (universal beams) are deeper and carry bending more efficiently, so they take over as spans grow, at the cost of depth below the ceiling.
Do I need building control approval to fit an RSJ?
Yes. Removing or opening a load-bearing wall is notifiable building work under the Building Regulations: you tell building control via full plans or a building notice, they check the engineer's calcs and the installed work, and issue a completion certificate at the end. Selling without one means regularisation later.
Sources
- gov.uk, building regulations approval
- gov.uk, Approved Document A (structure)
- steelconstruction.info, design codes and standards (BS EN 1993)
- SCI, the Blue Book: UK steel section properties
- legislation.gov.uk, Building Regulations 2010, reg 3 (meaning of building work)
- legislation.gov.uk, Building Regulations 2010, reg 16 (notice before work starts)
Two questions, then the right next step
See the typical section range, then get the calcs that count.
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