The beam size comparison tool is an educational comparison of listed UB sections. It no longer selects a “recommended” beam using an arbitrary capacity and safety multiplier.
What changes between rows
Your external line load and support-centre span stay constant. Each row adds the corresponding beam’s mass as self-weight and uses that section’s actual depth and major-axis second moment of area. This lets you see how section geometry changes the calculated elastic stress and deflection.
The last number in a UB designation is nominal mass, not a load rating. For 203×133×25 the tabulated mass is 25.1 kg/m and Iₓ is 2340 cm⁴. For 203×133×30 the values are 30 kg/m and 2896 cm⁴. These are distinct entries in the British Steel datasheet.
A useful comparison workflow
- Obtain a defensible external service line load and support-centre span.
- Enter the same assumptions for all sections; let the tool add self-weight.
- Choose an illustrative deflection target and inspect the entire table.
- Record candidate geometry constraints for discussion with your engineer rather than ordering the first row within the target.
A deeper section can change ceiling clearance and connection details. A heavier section can change handling arrangements. Neither issue is resolved by sorting results by mass. Steel grade and restraint conditions are not selected here because the tool does not perform the resistance checks that depend on them.
What to hand over for final selection
Give your engineer plans, load sources, section constraints and the proposed support locations. Request a drawing specifying grade, bearings, connections, fire protection and relevant construction responsibilities. Our methodology makes the calculator assumptions available for scrutiny, not as a substitute for that design.
Structural work requires a chartered structural engineer and the applicable Building Control approval. This educational article has not received an independent engineering review.