For CAN/CSA S16-01, S16-09, S16-14, BS 5950, Eurocode, and IS 800-07, sections are classified as Class 1 (Plastic), Class 2 (Compact), Class 3 (Semi-compact), or Class 4 (Slender) based on member dimensions and applied loads. For US and Australia design codes, sections are classified as compact, non-compact or slender. The following rules apply to the classification of all members (except for AS4100, where the effective section modulus is calculated for bending according to AS4100-98 Section 5.2):

• Cross sections are classified as plastic, compact or semi-compact. No consideration is given to slender (Class 4) sections. Sections of class 4 (slender) will be flagged and reported as an error.
• Sections subject to axial tension load only are classified as Class 1.
• Each element (flange, web) of a section is evaluated independently. The highest element class value will be assigned to the member as a whole.
• Any element (flange or web) required to resist axial compression load will be evaluated to determine into which class the element falls.
• Any element (flange or web) required to resist axial tension load only will be assumed to be class 1.
• Any element fully supported (e.g. a fully braced flange) will not be considered in determining the section class value.
• A flange element that carries tension due to bending moment will be Class 1 unless the section is under sufficient axial compression force to locate the plastic neutral axis within the tension flange. In this case the flange will be evaluated as if it were in complete axial compression.
• The flanges of a flange section subject to minor axis bending will be evaluated assuming full compression on each flange.
• Webs are considered as Class 1 if the section is only subject to axial tension or only minor axis moment (or a combination of these), otherwise the code evaluation rules are followed.
• Hollow rectangular sections subject to only minor axis bending (with or without axial load) will cause the ‘web’ of the hollow section to be considered as the flange, and the flanges to be considered as webs for class determination purposes.
• Double angles are always evaluated using the criteria for "Legs of single angle and double angle members with components separated" in table 7.