The population of Han Dynasty China in about AD1 is estimated as about 60 million; the land area was about 6 million km^2.

The population of the Roman Empire at the same time (the early empire under Augustus, with a land area of about 3 million km^2) is estimated as about 45 million (the later empire, larger (5 million km^2) and more populous is usually conservatively estimated at about 65 million for the mid-2nd century, with high estimates being as high as double that).

The Roman Empire wasn't Europe, since it didn't include all of Europe, but did include North Africa and part of Asia. The European population in AD1 is estimated at about 43 million (including European Russia, 31 million without it).

South Asia (India, Pakistan, Bangladesh) at the time: 46 million, over about 5 million km^2.

South-West Asia: 47 million, over about 6 million km^2 (which includes much desert).

The Chinese population was large, but not gigantic compared to other parts of the world. The South Asian population was similar to Roman, European, and SW Asian populations. The Roman population density appears to have been higher than the Chinese population density.

The population density of Europe was low, with an area of about 10 million km^2 (including European Russia and the Caucasus). The European population grew relative to the Chinese population over the Medieval period, with both European and Chinese populations being about 84 million in 1500 (so still a lower population density in Europe). The Chinese population pulled ahead in Early Modern times, in part due to the introduction of New World crops such as maize and sweet potatoes, but Europe again caught up by 1900.

For world populations by region over time, see Biraben, J.-N. (1979), "Essai sur l’évolution du nombre des hommes", Population 34(1), 13–27. https://www.persee.fr/doc/pop_0032-4663_1979_num_34_1_18032?pageid=t1_17