This article seeks to introduce a new methodological approach to estimate population size of settlements in the Graeco-Roman Fayum/Egypt (330 BC-400 AD). The aim is to represent and analyse the relationship of settlements and the facilities they provide. We suggest turning the information commonly contained in traditional site gazetteers into presence-absence matrices of selected facilities. We then use these facility matrices to estimate the size of ancient settlements through linear regression. The equation is initially tested on medieval settlements in Norwich and East Anglia (England) and later applied to a settlement-facility matrix for the Ptolemaic period (330-30 BC). The results from the medieval data show the validity of the approach with a complete data set. The circumstance that the Ptolemaic data is fragmented and incomplete naturally adds a small, but acceptable error to the estimates.