The length of snippets is dynamic, confirmed Google. The clarification come yesterday, by Danny Sullivan on Twitter, and reported by Search Engine Roundtable. Historically, Google had a limit of 165 characters in snippets (meta descriptions), but in the end of November 2017, beginning of December 2017, the snippets were updated to 320 characters.
This week, Google changed again most of the snippets lengths on search engine results pages (SERP) from 320 to about 155/160 characters.
“Our search snippets are now shorter on average than in recent weeks, though slightly longer than before a change we made last December. There is no fixed length for snippets. Length varies based on what our systems deem to be most useful,” said Sullivan.
John Mueller, from Google, said yesterday that these things “can always change over time (and by device, query, etc).” Google is “not announcing any fixed count as a target.”