When people say microbrewery or macrobrewery, they aren’t necessarily referring to the brewery’s size. They could very well be referring instead to the spirit or character behind the beer, not any actual output figures. For instance, when people disparage a particular beer as a macrobrew, they almost certainly don’t know how many barrels that brewery produces annually. Rather, they are more likely referring to the beer as perhaps uninspired and tasteless.
But you probably know this already, and what you really want to know is the objective distinction between microbreweries and macrobreweries. For that, we turn to the Brewer’s Association (brewersassociation.org), an organization whose purpose is to serve the interests of American craft brewers and the craft brewing community. The Brewer’s Association defines microbreweries as those that produce less than 15,000 barrels of beer annually and sell  75 percent or more of that beer off-site. It defines large breweries are those that produce more than 6,000,000 barrels annually.
So what about that huge gap? The Brewer’s Association calls those regional breweries, which produce between 15,000 and 6,000,000 barrels of beer per year. And that is why we began this response with an assumption about what people probably mean when they say micro or macro. You never hear anyone dissing regional breweries as such. If someone has something bad to say about a regional brewery, they probably employ the term macrobrewery.
Which leaves us with a decidedly vague distinction—and not much of an answer—if you are looking for a precise cut-off between micro and macro. You have some exact figures, but any precise distinction, if it exists, would appear somewhere in that huge swath of regional brewery gray area.
Because of this, we’re going to stick with what we think people mean when they say microbrewery or macrobrewery. When people who are unaware of the definition in terms of precise output say microbrewery, they likely mean a few things. To wit, the brewery:
As discussed, has an output that is pretty small compared to the big guys
Has a smaller target audience than the biggies
Seems to care more about the character of their beer(s), which themselves (the care and the character) are the selling point, without the need to employ beaches or beautiful women, etc.
The general idea behind macrobreweries on the other hand is if you make something on a massive scale for a huge audience, you need to remove a lot of the character. They are not  trying to make a beer without character or taste. They are trying to make a beer that the least number of people will dislike. A lot of people who prefer macrobrews probably don’t necessarily enjoy the taste itself, but rather the absence of certain tastes that they do not like—it’s not too hoppy, too malty, or too anything.
So the number of barrels aside, that leaves us with the fact that in common use anyway, microbrewery and macrobrewery are pretty imprecise terms. But at least their connotations are usually pretty clear.

SOURCES
http://www.brewersassociation.org/pages/business-tools/craft-brewing-statistics/market-segments