Indicative triage, not a design tool
Steel beam calculator: what size UK beam do you need?
Give the span and load for the section range typically specified on similar UK domestic jobs. Openings to about 3 m under a floor usually take 152x152 UC23 to 203x203 UC46. The real answer: an engineer's calculation for building control.
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.
Email me this result
We will send you these figures and a link back to them. One email, nothing else unless you tick the box.
Scope of this checker
The 5 things it checks
- 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 information site. 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 up to three firms, each 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.
| 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.
How this was compiled, and how to cite it
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.
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.
RSJ prices: how much does an RSJ cost in 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 for a 3m span? Sizes 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.
Structural calculations for building control: what a beam needs
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
Is this a free steel beam calculator?
Yes. The checker above is a free RSJ calculator for the first question, steel beam size. Enter the span and what sits above, and it shows the UC or UB range typically specified on comparable UK jobs. It is triage, not a design: the beam you fit still comes from a structural engineer's calcs.
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 4m span, or for a 5m span?
Floor-only spans of 3–4.5 m typically land between 203x203 UC46 and 254x146 UB37. 4.5–6 m spans use 254 to 305 series UBs, deeper with roof or masonry above. So what size steel beam for a 6m span? Floor-only, typically 254x146 UB37 to 305x165 UB46; beyond 6 m we give no range. Indicative 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, then issue a completion certificate. Selling without one means regularisation later.
Sources
This site's own dataset, every figure quoted from its source and dated:
- The UK Steel Beam Cost Index carries 7 published figures read from 7 sources' own pages; the 4 published figures given without a breakdown run from 75 to 1,200 GBP, read 11 November 2026.
- 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.
Put this on your site
<script src="https://steelbeamchecker.co.uk/embed.js" async></script>