Roman Numeral Converter (I, V, X, L, C, D, M)
Convert Roman numerals to numbers and back, 1–3999, with strict checking of the subtractive pairs and reference tables for the symbols, tens, hundreds and years.
The seven symbols
| Symbol | Value | Origin |
|---|---|---|
| M | 1,000 | mille — thousand |
| D | 500 | half of a thousand |
| C | 100 | centum — hundred |
| L | 50 | half of a hundred |
| X | 10 | ten |
| V | 5 | half of ten |
| I | 1 | one |
The six subtractive pairs
| Pair | Value | Reads as |
|---|---|---|
| CM | 900 | 100 before 1000 |
| CD | 400 | 100 before 500 |
| XC | 90 | 10 before 100 |
| XL | 40 | 10 before 50 |
| IX | 9 | 1 before 10 |
| IV | 4 | 1 before 5 |
These six are the only subtractions allowed. IL for 49 and IC for 99 look reasonable but are not standard — 49 is XLIX and 99 is XCIX.
1 to 20
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|
| I | II | III | IV | V | VI | VII | VIII | IX | X |
| 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
| XI | XII | XIII | XIV | XV | XVI | XVII | XVIII | XIX | XX |
Tens, hundreds and thousands
| Tens | Hundreds | Thousands | |||
|---|---|---|---|---|---|
| 10 | X | 100 | C | 1,000 | M |
| 20 | XX | 200 | CC | 2,000 | MM |
| 30 | XXX | 300 | CCC | 3,000 | MMM |
| 40 | XL | 400 | CD | 3,999 | MMMCMXCIX |
| 50 | L | 500 | D | ||
| 60 | LX | 600 | DC | ||
| 70 | LXX | 700 | DCC | ||
| 80 | LXXX | 800 | DCCC | ||
| 90 | XC | 900 | CM |
3 999 (MMMCMXCIX) is the largest number standard notation reaches, because M cannot repeat a fourth time.
Years in Roman numerals
| Year | Numeral | What it is |
|---|---|---|
| 1066 | MLXVI | Norman conquest of England |
| 1215 | MCCXV | Magna Carta |
| 1492 | MCDXCII | Columbus reaches the Americas |
| 1776 | MDCCLXXVI | US Declaration of Independence |
| 1789 | MDCCLXXXIX | French Revolution begins |
| 1888 | MDCCCLXXXVIII | The longest year — every symbol repeated |
| 1914 | MCMXIV | First World War begins |
| 1945 | MCMXLV | Second World War ends |
| 1969 | MCMLXIX | First Moon landing |
| 1984 | MCMLXXXIV | Orwell's title year |
| 2000 | MM | A short one — just MM |
| 2001 | MMI | A Space Odyssey |
| 2026 | MMXXVI | This year |
How Roman numerals work
Roman numerals are an additive system built from seven letters:I = 1, V = 5, X = 10,L = 50, C = 100, D = 500 andM = 1000. Write them from largest to smallest and add them up: MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1 = 2026. There is no zero, no negative number and no fraction — the system was built for counting and tallying, not for arithmetic.
M = 1000 · D = 500 · C = 100 · L = 50 · X = 10 · V = 5 · I = 1
The subtractive rule
Pure addition would need four symbols in a row for 4 (IIII), so a smaller symbol placed before a larger one is subtracted instead: IV is 4, IX is 9. Only six such pairs are legal — IV, IX, XL, XC, CD and CM — and the pattern behind them is strict. Only I, X and C may subtract, and each may only subtract from the next two symbols up. That rules out IL for 49 and IC for 99, which look plausible but are not standard form; the correct numerals are XLIX and XCIX. It also means I, X, C and M repeat at most three times, and V, L and D never repeat at all, since VV would simply be X.
Worked example
Take MCMXCIV. Read it in pieces rather than letter by letter: M is 1000, CM is 900, XC is 90 and IV is 4. Add them and you get 1994. Reading it as individual letters — 1000, 100, 1000, 10, 100, 1, 5 — gets you nowhere; the trick is spotting that a small symbol followed by a bigger one belongs with it. Going the other way, 1994 splits into 1000 + 900 + 90 + 4, and each part has exactly one representation, which is why the conversion is unambiguous in both directions.
Why 3999 is the ceiling
Since M is the largest symbol and no symbol may repeat more than three times, the largest writable number is MMMCMXCIX = 3999. The Romans handled larger values with a vinculum — an overline meaning "multiply by a thousand", so V̄ is 5000 — and with other notations that never fully standardised. Because the overline has no plain-text form and no single accepted set of rules, this converter stops at 3999 rather than guessing. If a numeral you have seen exceeds that, it is almost certainly using the overline convention.
Where you still meet them
Book chapters and preface pages, clock faces, monarch and pope names, film copyright dates, the Super Bowl, and the year on building cornerstones. Clock faces are the well-known exception to the rules above: many use IIII for four rather than IV, a convention usually explained by visual balance against the VIII opposite it. This converter follows the standard rules and will flag IIII as malformed, telling you what the standard form is.
Related
For binary, octal and hexadecimal — positional systems where the column matters rather than the symbol order — see thenumber base converter.
The system stops at 3,999
Standard Roman numerals have no symbol above M, so the largest value expressible in the usual notation is MMMCMXCIX — 3,999. Larger numbers historically used a vinculum, an overbar multiplying a numeral by a thousand, which has no agreed plain-text form and is not supported here. There is also no zero and no way to write a negative or fractional value: the system was built for counting and tallying, not arithmetic, which is part of why positional notation replaced it.