These are lists of regions and countries by their estimated real gross domestic product (GDP) in terms of purchasing power parity (PPP), the value of all final goods and services produced within a country/region in a given year.
Since pre-modern societies, by modern standards, were characterized by a very low degree of urbanization and a large majority of people working in the agricultural sector, economic historians prefer to express income in cereal units.
To achieve comparability over space and time, these numbers are then converted into monetary units such as International Dollars, a third step which leaves a relatively wide margin of interpretation.
This is because, in contrast to industrial economies, the average income ceiling of premodern agrarian societies was quite low everywhere, possibly not higher than twice the subsistence level.
[5] There was little difference in GDP per capita based on level of development in earlier eras, so in 1500, China was the largest economy in the world, followed closely by India.
"[8] Maddison's estimates have also been critically reviewed and revised by the Italian economists Giovanni Federico[9] and Elio Lo Cascio/Paolo Malanima (see below).
[13] The following estimates are taken from a revision of Angus Maddison's numbers for the whole of Europe by the Italian economists Elio Lo Cascio and Paolo Malanima.
Italic numbers not directly given by the authors; they are obtained by multiplying the respective value of GDP per capita by estimated population size.
In conclusion, the fact that the average incomes in the most developed agricultural economies like Augustan Rome and Basil's Byzantium were about twice or less than the subsistence minimum might indicate that the pre-industrial societies were unlikely to ever exceed that ceiling.