Maybe we should ask Mr. Owl.
Maybe we should make an effort to refrain from comments that don’t contribute to finding an answer to the question ?
Here’s an interesting bubble research site.
This article (PDF)
comes as close as I’ve found to an answer, but it’s for a slightly different system. With air bubbles in flowing water, the most common bubble size is ~50 micrometers. If that number is also good for bubble baths, the tub Chronos described would hold about a trillion (1X10[sup]12[/sup])bubbles.