In a 20 year career in the Air Force, on average how many different bases would you serve at?

There really is no average, unless you know the career field. Some folks move every 2-3 years, some folks can spend an entire career at one base. Some careers move more than others, some are world wide, some at limited locations. It's all in the luck of the draw.

I have friends who, by retirement, have been at 2 bases and others who have been at 10. Hubby, after 30 years, was stationed at 7.

6 or 7

By the time I hit 20, it will be 6 bases (actually 5 bases, I hit one twice).

I have seen some enlisted Airmen spend almost their entire careers at one base. Some officers PCS every two to three years, with some 1 year remotes mixed in.

The RCAF has some pretty long postings. Other than training, you might be at 2 or 3 bases in that time. Or, it could be more. In my 25 years, I was posted at least 7 times not including training, nor deployments. I served in 6 different places, but, some of them more than once, in different units.