That's a great question, and one I get a lot from friends moving into new apartments! From my experience living in the city, the hands-down most common size you'll see for the main kitchen trash can is the 13-gallon bin.
Think of those standard rectangular plastic cans with the swing lid—that's the 13-gallon workhorse. It strikes the perfect balance for urban living. It's large enough to hold a typical small household's bag of daily waste without needing constant emptying, yet it's compact enough to tuck into a kitchen cabinet, slide into a narrow slot between appliances, or fit neatly under the sink.
Why is this size so popular? A few key reasons fit the urban lifestyle. First, the standard tall kitchen trash bag you buy at any grocery store is designed for a 13-gallon can. It's a seamless match. Second, for most couples or small families in apartments, this size means taking the trash out every day or two, preventing odors from building up in tighter spaces. Finally, it aligns with many municipal collection rules where larger bins might be cumbersome for weekly pickup or for storing in small service alleys.
Of course, this isn't a one-size-fits-all answer. You might also see smaller 8-gallon bins in home offices or bathrooms, and larger 20-gallon rolling cans for shared building dumpster trips. But for the primary kitchen receptacle, the 13-gallon can is the undisputed champion of city homes. My advice? Start with a good 13-gallon can, and you can always add smaller specialized bins for recycling or compost later.