It's difficult to be exact about this, partly because we have no data, and partly because Antiquity is a very long period of time. Pella was only established as the new capital of Macedon in the early 4th century BC; it grew significantly after that, to a peak around 300 BC, only to decline once Macedon had been absorbed by the Roman Empire. By the 2nd century AD only a small village remained. However, this is based only on general statements found in ancient sources. We have no hard numbers. For example, Xenophon (Hellenika 5.2.13) says Pella was "the largest of all Macedonian cities" around 383 BC, but this doesn't really tell us anything about real size. With cities on which no census data survive, all we have to go on is the surface area of the archaeological site, the number of houses found, and so on. Inevitably, the archaological remains of a city will reflect its size at the time of its greatest expansion, even if traces of growth and contraction may remain.

On this basis, the Copenhagen Polis Project has classified Pella as a size 4 polis. The sizes defined by this project are very broad, meant to indicate ballpark figures; the categorisation of Pella as a size 4 polis means that its population is estimated to have been between 7,000-50,000, with a class average of about 17,000. This would be the total population of the city, including males and females, freeborn and slaves. Pella as a royal city may have inclined more toward the upper limit of its category, but little is known for certain.