Roman Numerals

How Roman numerals work

Unlike the modern (Hindu-Arabic) numeral system, Romans didn’t have digits (0-9) to represents numbers, so they used to use letters to code them. These are the seven letters used to write Roman numerals, and their corresponding value in Arabic numerals: I=1, V=5, X=10, L=50, C=100, D=500, M=1000

Reading and writing Roman numerals isn’t difficult. You just need to know the value of each letter and a couple of simple rules.

The basic rule is this: To read a Roman number, just add the values of its letters:
III 1 + 1 + 1 = 3
VI 5 + 1 = 6
XVII 10 + 5 + 1 + 1 = 17
XX 10 + 10 = 20

Subtractive notation: As an exception to the above rule, when a letter precedes another of greater value, then it is not adding, but subtracting. Some examples:
IV 5 – 1 = 4
IX 10 – 1 = 9
XIX 10 + (10 – 1) = 19
XL 50 – 10 = 40
CM 1000 – 100 = 900

To write any number, just translate separately each decimal place, from left to right: the thousands, hundreds, tens and units. 39=30 + 9 → XXX + IX → XXXIX
140=100 + 40 → C + XL → CXL
2018=2000 + 10 + 8 → MM + X + VIII → MMXVIII

The principle of brevity: You should always use the minimum number of letters necessary for each of the decimal places separately (but not for the whole number). For example:
5 → IIIII → V
9 → VIIII → IX
44 → XXXXIIII → XLIV
95 → VC → XCV
999 → IM → CMXCIX

Now you are ready to take any of our quizzes on Roman numerals. You can choose between three levels of difficulty:

Alternative forms

While the above rules are the “standard” nowadays, they have not been consistently used in the past. For example, it is possible to find ancient documents and inscriptions using non-standard Roman numerals such as IIII (4), IC (99), IIXX (18) or MDCCCCX (1910).

Millions in Roman numerals

Although Romans didn’t usually have the need for large numbers, they adopted a variety of conventions for this. One of the most popular (at least, in the Middle Ages) was a horizontal line, or vinculum, to multiply by one thousand.

Some authors suggest that a double line would thus represent multiplication by one million, although there is no evidence that it was ever used in practice. For convenience, though, our Roman numeral converter follows this convention (in case you really need to translate such big numbers!).

What about zero?

The Roman numeric system didn’t have a specific Roman numeral for zero. For this, they simply used to write the word nulla (none), nihil (nothing) or just the letter N.

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How are Roman numerals used today?

Roman numerals were used until the high and late Middle Ages, when Arabic numerals were gradually introduced in the Western World.

Nowadays, Roman numerals are used only in certain contexts, like:

• In series of popes, emperors or monarchs with the same name (Elizabeth II). These are called regnal numbers.
• To name dynasties in certain cultures (Dynasty XVIII of Egypt).
• In monuments or commemorative plaques, to indicate a year.
• To mark the hours in clock faces.
• To enumerate books, volumes, chapters, etc., in literary works.
• To enumerate pages in preliminary chapters of books (like the prologue).
• For recurring events such as congresses, festivals or championships (Super Bowl LIII).
• Some series of names of products or titles of movies (Mac OS X, Rocky IV).
• As generational suffixes (like Patrick II instead of Patrick Jr.).
• For the year in copyrights of some movies or TV shows (e.g., © mmxviii).

In Spanish, there are two additional uses:

• Centuries are always written with Roman numerals (21st century → siglo xxi).
• In short dates, the month can be written with Roman numerals (12/25/2018 → 25/XII/2018).

Try using our Roman Numerals Date Translate Tool

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Roman Numerals Date Translate Tools

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References

• Ifrah, G. and Bellos, D. (2000). The universal history of numbers. New York: Wiley.
• Smith, D. (1958). History of mathematics. New York: Dover Publ.
• Números. (2005). In: Diccionario panhispánico de dudas, 1st ed. [online] Real Academia Española.

Arabic	Roman
1	I
2	II
3	III
4	IV
5	V
6	VI
7	VII
8	VIII
9	IX
10	X
11	XI
12	XII
13	XIII
14	XIV
15	XV
16	XVI
17	XVII
18	XVIII
19	XIX
20	XX
21	XXI
22	XXII
23	XXIII
24	XXIV
25	XXV
26	XXVI
27	XXVII
28	XXVIII
29	XXIX
30	XXX
50	L
100	C
500	D
1000	M
1 – 50…
1 – 100…
1 – 1000…
1 – 10000…