When should I use ‘et al.’ in IEEE citation format?

In IEEE citation format, you should list the names of up to six authors in a reference on your IEEE reference page. If the source has seven or more authors, just list the first author’s name followed by ‘et al.’ (in italics): ‘F. Gupta et al., …’

In the main text, if you mention a source with three or more authors, you should use ‘et al.’: ‘Fowler et al. [11] argue that …’

Note that you’re not required to mention author names at all in the text though – just the IEEE in-text citation number is enough, in which case ‘et al.’ isn’t needed: ‘[11] argues that …’