Of course, the value of the sesterti must itself have fluctuated over the centuries it was in use. And so if I must narrow it down, I am particularly interested in its value during
- the time of Lollia Paulina who was once covered with 40M sesterces' worth of jewels; and
- the time of Cleopatra, who once drank a dissolved pearl worth 10M sesterces,
both of these stories being from Pliny, Book 9, Ch. 58.
Adam Smith writes in The Wealth of Nations:
When we read in Pliny, therefore, that Seius bought a white nightingale, as a present for the Empress Agrippina, at a price of six thousand sestertii, equal to about fifty pounds of our present money; and that Asinius Celer purchased a surmullet at the price of eight thousand sestertii, equal to about sixty-six pounds thirteen shillings and fourpence of our present money
Smith also writes:
Three sestertii, equal to about sixpence sterling,
which would be consistent with the previous quote, since £1 = 240p.
So according to Smith, 6,000 sestertii ≈ £50 "of our present money". The Wealth of Nations was first published in 1776. Using the Bank of England's inflation calculator, £50 in 1776 = £7,519.57 in 2016, or about US$10,000 at current conversion rates (according to Google).
So 6,000 sestertii ≈ US$10,000 in 2017 or 1 sesterti ≈ US$1.67? Thus
- Lollia Paulina's jewels (40M sesterces according to Pliny) would be worth US$66.7M today? And
- Cleopatra's swallowed pearl (10M sesterces according to Pliny) would be worth US$16.7M today?
Of course, I have no idea how Adam Smith did his conversion, but presumably some modern day historians/economic historians have since done better.