RSJ Sizes UK: Beam Size Chart by Span and Load-Bearing Wall Guide

RSJ Sizes in the UK

RSJs are now specified as Universal Beams (UB). A size such as 203x133 UB25 tells you:

203 — depth of the section in mm
133 — width of the flange in mm
UB25 — weight in kg per metre (heavier means thicker steel and more capacity)

Indicative RSJ Size Chart by Span

The table below shows the typical order of size an engineer might land on when removing a single load-bearing wall in a standard two-storey brick house where the wall carries a floor above. It is for understanding only — not for design.

Clear span	Typical beam range
Up to 2.5m	152x89 UB16
3m	152x89 UB16 – 178x102 UB19
4m	178x102 UB19 – 203x133 UB25
5m	203x133 UB25 – 254x146 UB31
6m	254x146 UB31 – 305x165 UB40

Add a wall above, a roof load, a chimney or a point load from a post and the beam can jump one or two sizes.

Load-Bearing Wall Size: Why Thickness Is Not Enough

Searches for a "load bearing wall size chart" usually assume the wall's thickness decides the beam. It does not. The beam is sized from:

Span of the new opening
Loads above — floors, roof, internal walls, chimneys
Bearing length at each end and the strength of the supporting masonry
Deflection limits so ceilings do not crack
Padstones or columns needed to spread concentrated loads

Why a Chart Will Not Pass Building Control

Building Control require calculations specific to your property. They also protect you at resale — your buyer's solicitor will ask for them.

Next Steps

SBS provides fixed-fee beam calculations across Ilford, Redbridge, Newham, East London, Tilbury, Grays and Thurrock.

📞 Call 07401 650600 or email us with a photo and span for a same-day quote.

Frequently Asked Questions

What are the common RSJ sizes in the UK?

Common domestic universal beam sizes include 152x89 UB16, 178x102 UB19, 203x133 UB25, 203x133 UB30, 254x146 UB31 and 254x146 UB37. The first numbers are the section depth and width in millimetres and the last number is the weight in kg per metre.

What does 203x133 UB25 mean?

It is a Universal Beam roughly 203mm deep and 133mm wide that weighs about 25kg per metre. A heavier beam of the same depth (for example UB30) has thicker steel and carries more load.

Is there a load bearing wall size chart?

There is no single chart that works for every house. Wall thickness tells you little about the load — floors, roof, chimneys and walls above all matter. Span tables are only indicative; a calculation is needed for Building Control.

Can I use a beam size chart instead of calculations?

No. Building Control will reject a beam chosen from a table. Calculations must be specific to your property and loads.