• Micro-enterprises: enterprises which employ less than 10 people and whose annual turnover or annual total balance does not exceed EUR 2 million;
• Small enterprises: enterprises employing between 10 and 50 people and whose annual turnover or annual total balance does not exceed EUR 10 million;
• Medium-sized enterprises: enterprises employing between 50 and 250 people and whose annual turnover does not exceed EUR 50 million or annual total balance does not exceed EUR 43 million.
• Large enterprises: enterprises which employ 250 people or more and which achieve an annual turnover or annual total balance above the threshold of medium-sized enterprises.

Source: European classification defined by “Raccomandazione n. 2003/361/CE della Commissione Europea", document available at this link