Some friends did this back when Google first switched to truncating by pixel count rather than character count. They've updated it the best they can through all of the recent vagaries.
Anyway, it makes a pretty good estimate of where Google would truncate if they actually deign to use your title and description, including bolding the search terms and things like that which affect truncation.
I find myself editing a bunch of metas and using it, so thought I'd pass it on
https://mcculloughwebservices.com/2016/07/04/title-tag-length-meta-description-length-tool-2016/