If across 22 valid answers your brand appears 8 times, competitor A 14 times and B 6 times, there are 28 mentions in total and your share is 8 of 28.

Two conditions: the set of competitors is decided before measuring, and one answer can mention several brands, so the share says how often each one appears, not who “wins” each answer.

Like the mention rate, it describes a sample. It is not market share.

Read: How to know if ChatGPT recommends your company.