There are no set in stone definitions for craft brewery, micro-brewery or nano-brewery.
First off, a brewery is a place that makes beer. Breweries brew beer in "batches" like a batch of cookies. Each batch produces a set number of gallons or barrels of beer. The size of each batch is limited by the size of the equipment available to the brewery. Long Trail Brewery produces in the ball park of 100,000 barrels (3million gallons) of beer every year. Each batch is brewed in a 60barrel automated brewing system. The brewery consists of several brewing systems which, for the most part, are run at least once a day. This means Long Train Brewery and other similar breweries (like Magic Hat, Otter Creek) can be called a "Craft" brewery since they do produce less than 6million barrels of beer annually.
Now, Long Trail is just an example. It is mostly regionally consumed, but distributes to several states outside of Vermont. By comparison, a micro-brewery produces about 10% of the yearly output of Long Trail. Meaning what Long Trail Brewery outputs in 2months is more than the yearly output of the largest micro-brewery.
A micro-brewery typically uses between a 30 to 60 barrel brew system. The brewery typically only has one brew system, unlike Craft breweries which can have several brewing systems. At a micro-brewery the system will produce about one batch of beer a day to one batch of beer every other day. Several micro-breweries still produce beers on a 15barrel system at the rate of one batch every other day for a total of 3,000 barrels a year. This is 3,000 barrel output is close to the output of a nano-brewery. A nano-brewery usually uses a 7.5barrel systems (1/3 to 1/10th the size of a microbrewery) and produces beer at the rate of a few batches a week. This puts the total output of a nano-brewery at 1,000 barrels per year.
How does this compare to a brew pub? A brew-pub typically produces 15,000 or less barrel of beer each year and 75% or more of the beer is consumed at the pub (not sold to other pubs). A typical brew pub produces beer on a 3-7.5 barrel system at the rate of one batch every few days. This means a brew pub and nano-brewery produce about the same volume of beer each year.
What is a pico brewery? A pico-brewery is smaller than a nano-brewery. The common definition for pico-brewery is a brewery that uses a 1-3bbl system. If a pico brewery produces beer every other day (which is considered very high output for a pico-brewery) they will produce just over 500barrels a year. By comparison this is the 2 day output of breweries like Magic Hat and Long Trail.
How does this compare with a home brewer? First off, the above are licensed breweries. Second, a home brewer is legally allowed to make UP TO 200 gallons of beer each year for personal consumption without acquiring state and federal licensing. At roughly 30 gallons to the barrel, the home brewer can only produce 6.6 barrels of beer each year (a fraction of what Long Trail produces in just 1 batch). Most home brewers produces beer in 5 gallon batches also refereed to as a sixth (1/6) barrel. In addition, most home brewers do not run their brewing equipment every day. Instead a home brewer will make a batch at a rate of every other week or less.
What is a femto-brewery? This is a term coined by North Williston Brewing to define the home brewer who hits the 200gallon mark annually. This is not a licensed brewery. The beer produced by North Williston Brewing is for personal consumption only. Well, family and friends are always welcome to stop by to share in some great, usually high quality, but always hand crafted home-brew.