Roman numerals: rules, table and how to convert them
Seven letters and four rules are enough to write any Roman numeral from 1 to 3999. What trips people up is not the conversion, which you can do in parts without memorising anything, but the exact rules: why 49 is XLIX and not IL, how many times a letter can repeat. The complete rules, checked against the Royal Spanish Academy's reference, and a method for converting by hand.
The seven letters
Roman numerals use seven letters of the Latin alphabet, each with a fixed value:
| I | V | X | L | C | D | M |
|---|---|---|---|---|---|---|
| 1 | 5 | 10 | 50 | 100 | 500 | 1000 |
The rules
These are the writing rules set out in the Diccionario panhispánico de dudas of the Royal Spanish Academy (RAE):
- Addition. When a symbol is followed by one of equal or lower value, they add: VI = 6, XV = 15, XXVII = 27.
- Subtraction. When I, X or C is followed by a higher symbol, it is subtracted: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900.
- Who can subtract. Only I, X and C, and only before the next two symbols: I before V and X; X before L and C; C before D and M. That is why 49 is XLIX and not IL. V, L and D never subtract: 45 is XLV, not VL.
- Repetition. A symbol is not repeated more than three times in a row: 333 is CCCXXXIII, but 444 is not CCCCXXXXIIII but CDXLIV. Nor is a symbol repeated if another is worth the same on its own: 10 is X, never VV. That is why V, L and D are never repeated.
The one current exception to the three-repetition rule is the IIII found on the faces of some clocks.
How to convert a number to Roman, in parts
The most reliable method is to write each digit separately (thousands, hundreds, tens and units) and join them, left to right. This table gives the pattern for each position:
| Digit | Units | Tens | Hundreds | Thousands |
|---|---|---|---|---|
| 1 | I | X | C | M |
| 2 | II | XX | CC | MM |
| 3 | III | XXX | CCC | MMM |
| 4 | IV | XL | CD | — |
| 5 | V | L | D | — |
| 6 | VI | LX | DC | — |
| 7 | VII | LXX | DCC | — |
| 8 | VIII | LXXX | DCCC | — |
| 9 | IX | XC | CM | — |
Examples: 2026 = 2 thousands (MM) + 0 hundreds + 2 tens (XX) + 6 units (VI) = MMXXVI. 1999 = M + CM + XC + IX = MCMXCIX. 444 = CD + XL + IV = CDXLIV. Positions with a zero are simply left out.
How to convert Roman to a number
Read left to right adding each value, except where a symbol is smaller than the next one: then it is subtracted. With MCMXCIV: M (1000) + CM (900) + XC (90) + IV (4) = 1994.
The current years
| Year | Roman |
|---|---|
| 2020 | MMXX |
| 2025 | MMXXV |
| 2026 | MMXXVI |
| 2027 | MMXXVII |
| 2030 | MMXXX |
| 2050 | MML |
| 2100 | MMC |
The 3999 limit and how it is exceeded
With the seven letters, the largest number that can be written is 3999 (MMMCMXCIX), because four Ms in a row are not allowed. For larger values, the RAE rule is that a Roman numeral's value is multiplied by a thousand for each horizontal bar drawn over it: a bar over the M is a million. It is a rare usage, almost gone from everyday writing.
Where they are still used
According to the RAE, today they are used almost always as ordinals and in a few cases. In English the same uses apply:
- Monarchs, popes and emperors of the same name: Elizabeth II, John Paul II, Napoleon III. Always after the name.
- Congresses, championships, festivals and events: the Games of the XXXIII Olympiad (Paris 2024). Before the noun.
- Volumes, books, chapters, acts and scenes: volume III, chapter IV, Act II. After the noun.
- Preliminary pages of a work (preface, introduction): page xvii of the preface.
- Dynasties, years on monuments and plaques, volume years of periodicals, and the degrees of the Mercalli earthquake scale.
Roman numerals are written in capital letters today. The exception is list numbering in lower case (i, ii, iii, iv), often called “romanitos” in Spanish.
How they are read
In English, Roman numerals for monarchs and popes are read as ordinals (Henry VIII is “Henry the Eighth”, Elizabeth II is “Elizabeth the Second”), and numerals for volumes, chapters and similar can be read as cardinals or ordinals (“chapter five”). Years are read as the ordinary number: MMXI is “two thousand eleven”.
A common trap when turning a year into a century: strictly speaking, since there is no year 0, the 21st century runs from 2001 to 2100 and the year 2000 belongs to the 20th century; in popular usage it is usual to group 2000 to 2099. It is worth knowing if the answer matters.
Converting without the sums
The Roman numeral converter works both ways, from 1 to 3999, and shows how each number is put together. If what you want is to write a number out in words (for a cheque or a contract, say), there is the number to words tool. Both run in your browser.
Sources and further reading
- RAE and ASALE: Diccionario panhispánico de dudas, “números” (section 2: Roman numerals, spelling, use and reading)
- Wikipedia: Roman numerals (3999 limit and writing conventions)
- Wikipedia: Century (how centuries are counted: strict and popular usage)
Figures checked on 3 October 2026.
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Frequently asked questions
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