RSJ Beam Estimator
Calculate beam lengths and weights for structural openings.
Steel Material
Structural Strength: The UK Steel Guide
Total Beam Length
Removing a load-bearing wall is the most common way to create an open-plan living space in the UK. The steel beam (often called an RSJ or Rolled Steel Joist) must be long enough to sit securely on the supporting walls at either end.
Our **RSJ calculator** ensures you don't just order the width of the hole. It automatically adds the standard **150mm bearings** required by UK Building Control, helping you estimate the true weight and cost of the material.
Standard Terminology
Lifting & Logistics
Steel is incredibly dense. A standard 3-metre beam can easily weigh over **75kg**, making it dangerous to lift without proper equipment. If your project requires multiple steels or a beam over 100kg, you will need a **Genie Lift** or 'Strongboys' to safely position the beam.
Always ensure the steel is 'chocked' and leveled before the mortar in the padstones sets. Once in place, the steel must be encased in fire-rated plasterboard (usually two layers) to meet safety regulations.
Fire Protection
Steel loses its structural strength very quickly in a fire. You must protect it using **intumescent paint** or, more commonly, by boxing it in with fire-resistant plasterboard (Pink board) to provide a 30 or 60-minute fire rating.
Point Loads
A steel beam creates 'point loads' at either end. It is vital that the wall supporting the beam is capable of taking this concentrated weight. Your structural engineer will check the wall and foundation directly beneath the bearings.
Pro Tip: The 15mm Gap
When ordering your steel, don't forget that it will be cold. In the winter, steel can contract slightly. Pros often leave a **10-15mm gap** at one end of a very long run to allow for thermal expansion and to make fitting the beam easier between two fixed walls.
RSJ & Steel Sizing FAQ
Critical Disclaimer
This tool is for material estimation ONLY. Sizing a steel beam is a complex engineering task involving 'Loading', 'Deflection', and 'Shear' calculations. **You MUST consult a qualified structural engineer** to specify the exact beam required for your home.