In everyday US usage, "cities" are usually bigger than "towns." But you cannot get precise about it. Usually, a major metropolitan area--one that is famous enough for people in other countries to know about--is called a city. New York, Los Angeles, Washington, D.C. are "cities." If the only thing you know is the word "city," you think of skyscrapers, noise, traffic, museums, hotels, busses, and concrete and pavement everywhere--except for big and little "parks." You think of a population of a million or more. "Town" means "anything too small to be called a city." Where it gets complicated is that in the United States, there are legal definitions of the terms. Those legal definitions are state law and vary! Very roughly, if it is run by a "mayor," it is a "city;" if not, it is a "town. Thus, Newburyport, Massachusetts, population 17,000, is run by Mayor Donna Holaday, so it is officially "the City of Newburyport." The town of Brookline, Massachusetts has a population of 58,000, but is a "town" because it has no mayor--it has a "representative town meeting" form of government. In ordinary life people don't pay attention to these technicalities, but may refer to the official names of their own municipalities because they see them on tax bills, etc. Someone living in Newburyport might say "I see the city tax bill just came," but talking to a stranger would say "I live in Newburyport, a lovely town on the coast of Massachusetts." "Town" is used as a casual, familiar, or affectionate way to refer to a city. For example, you might say "I'll see you the next time I'm in town" even if the "town" is New York City. Similarly, locales within a city are referred to as "uptown" and "downtown." A song celebrates "New York, New York, a helluva town" and another one celebrates "Chicago, that toddlin' town." Wherever you grew up is "my home town."

A lot of my students ask this question... so I think I can help! Generally this is the rule: Large city - a city with a large population and many services. The population is less than 1 million but over 300,000. City - a city would have abundant services, but not as many as a large city. The population of a city is between 100,000 and 300,000 people. Large town - a large town has a population of 20,000 to 100,000. Town - a town has a population of 1,000 to 20,000. In the UK, traditionally 'city status' was awarded to those places with a cathedral. However, this is not the case nowadays. You now have to apply for 'city status' and once granted, you can still lose it.