The outside diameter is generally said to be 15" in diameter. I don't on the gauge thickness of a keg but you can bet the inside diameter is just shy of 15". Sorry, guess that's not all that helpful. If you're trying to determine false bottom sizing, though, I bet there are several people here that can tell you what you need. The Sankey false bottom NB sells is only 11.5" in diameter, which i guess works out due to the dished bottom of the keg.