Many documents, for example, land records used Roman numerals. You can see them on many old buildings, and they are used today sometimes in film credits to say what year the film was made. It looks far more impressive to see MCMXCVIII, rather than 1998. Conversion of Roman numerals to our system helps demystify, especially when it’s a film! In fact, try to get your children or grandchildren to read the time on an analogue clock with Roman numerals.
It is also useful to have a go at converting our numbers to Roman numerals, simply because it helps in understanding Roman numerals. It is hard to conceive how the Romans managed to build such large edifices as the Colosseum and put such such a huge dome on the Pantheon with a numbering system based on letters, and which does not include zero.
Here are the letters of the alphabet the Ancient Romans used to express numbers. The table below shows the numerals that were used and their value.
The system is simple, when you know how: to write Roman numerals that are not multiples of 5, the Romans simply added I, except for 4, 9, 14, etc, when they subtracted I from the next multiple of 5, so you get:
A similar pattern occurs around the number 50, but note, you can only subtract a power of ten, and only from the next two “numerals” that are higher in rank to the letter to be subtracted. Remember, Roman numerals that symbolise numbers are I, V, X, L, C, D, and M.
I can be subtracted only from V and X. X can be subtracted only from L and C. C can be subtracted only from D and M.
You CANNOT subtract I from C to get 99. 99 must be written XCIX.
It is easier to read Roman numerals than it is to write them. The one rule that must be remembered is that if a numeral precedes another numeral that is larger than it, the first numeral is taken from the second. This is shown in a number of examples above. For instance, 49: XLIX. L is 50, but XL is 40 – X (10) is taken from L (50) to make 40, and similarly with IX, I (1) is taken from X (10) to make 9.
There are several websites (including Wikipedia) that can provide more detail, but if you just want a quick and accurate Roman numeral converter, try