This quote is from a report, which itself is based on a FAO report: http://www.fao.org/3/ca7036en/ca7036en.pdf Quote with context: The results show that, worldwide, farms of less than 1 hectare account for 70 percent of all farms, but operate only 7 percent of all agricultural land. Slightly larger farms between 1 and 2 hectares account for 14 percent of all farms and control 4 percent of the land. Together, farms of…
In the US, the sale of public lands for everything west of the Ohio River was on the basis of the Public Land Survey System. The smallest saleable parcel was a "quarter-quarter section", or 40 acres (~16 hectares) of land. The Homestead Acts would grant (at various times) 160, 320, or 640 acres of land to free for anyone who would farm out. In other wards, the "small" pioneer farms of American history are in the top 1% of all farms.
Put differently, the large number of small farms is driven by the size of subsistence farms in the intense rice-growing areas of Southeast Asia (rice being more productive per acre than wheat, especially if you're not dealing with industrial inputs). Then, you have the subsistence farms of less-productive crops like wheat, mostly in Africa.