A Bum or Two or Three

My SIL measures the size of kitchen in bums.  She has a two-bum kitchen maximum capacity.  My grandma's kitchen was a one-bum kitchen, for sure.  Mine is much larger:  I'd say it's a four-bum kitchen.

But the hallways between our cubicles at work?  One and a half bums.  Two if both people are skinny.

We need a passing lane.