Every UK steel section is named by its shape and a few key dimensions. The order of the numbers depends on the type of section.
Universal beams and columns (UB, UC)
A 203x133x25 UB is a universal beam with a nominal depth of 203 mm, a nominal width of 133 mm and a mass of about 25 kg per metre. The same pattern is used for universal columns, such as a 152x152x23 UC. The first two numbers are the "serial size"; within one serial size there are several weights, with thicker flanges and webs making the heavier ones slightly bigger.
Channels (PFC)
A 150x75x18 PFC is a parallel flange channel 150 mm deep, 75 mm wide and about 18 kg per metre. Channels are often used for trimmers, edge beams and lintels.
Angles (RSA, EA, UA)
Angles are named by their leg lengths and thickness: 100x100x10 EA is an equal angle with 100 mm legs, 10 mm thick. An unequal angle such as 150x90x10 UA gives the long leg first.
Hollow sections (SHS, RHS, CHS)
Box sections are named by their outside size and wall thickness: 100x100x5 SHS is a 100 mm square hollow section with a 5 mm wall; 150x100x6 RHS is rectangular. Circular tube is named by outside diameter and wall, such as 114.3x5 CHS. Hot-finished (BS EN 10210) and cold-formed (BS EN 10219) hollow sections look similar but are not interchangeable without the engineer's approval.
Flat bar and plate
Flat bar is width x thickness, for example 100x10 FB. Plates are usually given as thickness first or as "PL10", with the plate size shown on the drawing.
The steel grade
Most drawings also give a grade, such as S355J2. The 355 is the minimum yield strength in N/mm²; the letters describe toughness. Our guide to S275 and S355 steel grades explains them.
Old imperial sizes
Older drawings and builders may still talk about an "8 by 4 RSJ". That was an 8 inch by 4 inch rolled steel joist; the nearest modern section is around a 203x102 UB. Our guide on RSJ vs universal beam covers the history.
Use the section finder to search sizes by depth and weight, or browse the full steel size tables.