The most common way to measure farm size is by the value of gross farm sales. Acreage is not used for comparisons across differing kinds of farms because in some cases a farm need not have land (i.e., bee hives may be in constant rotation among parcels not belonging to the beekeeper). There are about 2.1 million farms in the United States. For 2003, according to analysis by the Economic Research Service, commercial farms, which include those having sales of $250,000 or more annually, constituted 9% of all farms and accounted for nearly 72% of production. Intermediate farms constituted 24% of all farms and accounted for 19% of production. The largest number of farms, characterized as rural residence farms, constituted 68% of all farms and accounted for 8% of production.