Ranges are between the high 60's% and can be as high as the low 90's% at top tech companies like the ones you have mentioned. I am defining conversion to mean "eligible to convert to full time employment"and not just eligible for an internship the next year.

The conversion number fluctuates based on the quality and performance of students that particular year, as well as well as available headcount. For the companies that you have mentioned, in the current market, headcount is less of an issue. I'm fairly confident that if every single eligible intern had a strong performance, and was a good fit for the company, they would want to hire them full-time.

At Google, when a team gets an internship it comes with a full-time role that the intern can convert to. However, the intern's performance and interviews aren't always strong enough to make the case for conversion.