Roman Coin Denominations

Thought out it's history the values of Roman coins changed several times. Here are two web sites that will help answer your question,
http://www.unrv.com/enconomy/roman-...inations.php
http://dougsmith.ancients.info/denom.html

As Doug Smith said on his site, there are some Roman coin types for which we simply do not know what name the Romans themselves gave them, because no record giving a name (either an official name or a nickname) to that specific denomination has survived.

The coin which we call the antoninianus, for example - we call them that because an emperor named "Antoninus" (who is better known by his nickname, Caracalla) was the first to issue them. We assume their face value was 2 denarii, but we don't even have any hard evidence that this is indeed the case; over the nearly 100 years they were issued, nobody wrote their name down where we would find it.

Likewise for the various denominations of copper coins of the post-Constantine period - the combination of inflation and political instability created a bewildering array of sizes, with no clear-cut differences between denominations that are obvious to us today. We simply call them "Late Roman Bronzes" and distinguish them by size, with "AE1" being large down to "AE4" being tiny. All the records that survive use the generic word "nummus" (coin). By the time stability returns in the early Byzantine period, "nummus" was the actual de facto name given to the smallest bronze coins, and the new larger bronzes were given face values in multiples of the nummus.

When you move into the Roman Provincial and Greek series, our knowledge of the names given to the various bronze coins is scant indeed. In most of these cases, numismatists usually don't bother to try to give them names and simply identify them by their diameter in millimetres; for example an "AE26" is a bronze coin 26mm or 1 inch across.

Some of the Roman Provincial coins from the Balkans area have the numerical demonimation on them and generally these are referred to as assari or assarion (sl.), though again that is an imposed name rather than a contempory one. It's quite usual to see coins described as those denominations - e.g, 5 assari or 2 assari etc. Larger coins issued under Gordian III, for example, can be as high as 12 assari, though the physical sizes of these larger coins tend to be similar to the Imperial Asses