Roman numeral converter
Type a number or a Roman numeral and the other side fills in, with a breakdown of how it is built.
Runs entirely in your browser
Result
Breakdown
Symbols
| Symbol | Value | Subtractive pair |
|---|---|---|
| I | 1 | IV = 4, IX = 9 |
| V | 5 | never subtracted |
| X | 10 | XL = 40, XC = 90 |
| L | 50 | never subtracted |
| C | 100 | CD = 400, CM = 900 |
| D | 500 | never subtracted |
| M | 1000 | no larger symbol |
Years to try
Standard numerals cover 1 to 3999. An optional extended range reaches 3,999,999 using the overline (vinculum) for thousands. Roman numerals have no zero, no negatives and no fractions here.
How to convert Roman numerals
- Type a whole number from 1 to 3999 into Number, or a Roman numeral such as
MCMXCIVinto Roman numeral. Lowercase is fine. - The other box fills in as you type, and the breakdown below shows how the symbols add up, for example M + CM + XC + IV.
- If a numeral is not valid, the message says which rule it breaks and what the usual form is. Tick the extended range to go beyond 3999.
How Roman numerals work
Roman numerals are an additive system with one twist. Symbols are written from largest to smallest and their values are added: XVI is 10 + 5 + 1 = 16. The twist is the subtractive pair: a smaller symbol placed immediately before a larger one is taken away from it, so IX is 10 − 1 = 9. Only six pairs are used (IV, IX, XL, XC, CD and CM), and that restriction is what makes the standard form unique, with exactly one numeral per number.
A reliable way to write any number is to take it one decimal place at a time. 1994 is one thousand (M), nine hundred (CM), ninety (XC) and four (IV), which is MCMXCIV. Reading is the reverse: scan left to right, add each symbol, and subtract it instead when the next symbol is larger. The breakdown under the converter shows each of these pieces so you can follow the arithmetic.
Because the largest everyday symbol is M, the strict system tops out at 3999 (MMMCMXCIX); a fourth M would break the three-in-a-row limit. Larger values were written in various ways, including a bar over a symbol to multiply it by a thousand. That bar, the vinculum, is a later convention and not used consistently, which is why the extended range here is optional. Roman numerals are still found on clock faces, building cornerstones, film copyright dates, book prefaces and the numbering of sequels and sporting events.
Tips
- Working out the date of an anniversary or a deadline before engraving it? The date calculator adds years, months and days.
- Curious how other number systems look? The number base converter shows binary, octal and hexadecimal.
- For arithmetic on the decimal numbers you decode, open the scientific calculator.
Questions
Why is 4 written IV and not IIII?
Standard modern numerals never put the same symbol more than three times in a row, so 4 is written as 5 − 1, that is I before V. The same idea gives IX for 9, XL for 40, XC for 90, CD for 400 and CM for 900. IIII does turn up on old clock faces and in some medieval texts, but it is not part of the strict form this tool checks.
Which combinations are rejected and why?
IIII and MMMM (a symbol four times), VV (V, L and D are never doubled), IC and XM (I may only precede V or X, X only L or C, and C only D or M), VX (V, L and D are never subtracted), IIX (a subtracted symbol appears once) and MCMC (a symbol that has already been subtracted from cannot be added again). Each rejection names the rule and gives the standard form of the value when it is clear.
What is the Roman numeral for 0?
There is none. The Roman system had no symbol for zero, as it had no need to count 'nothing' in a place-value column. Medieval scribes sometimes wrote the Latin word nulla or an N where a table needed it, but no zero symbol was part of the numerals themselves.
How do I write 4000 and larger numbers?
Tick the extended range. A line over a symbol (a vinculum) multiplies it by 1000, so 4000 is I̅V̅, 5000 is V̅ and 1,000,000 is M̅. The tool writes the overline as a combining character, and accepts square brackets as an easy way to type it: [IV] means I̅V̅. This is a later and less standardised convention, so other sources may write large numbers differently.
Does it accept lowercase?
Yes. mmxxvi is read as MMXXVI, and the result shows the capitals. Spaces are ignored. Letters outside I, V, X, L, C, D and M are reported by name.
How do I write a year such as 2026?
Split it by place value: 2000 is MM, 20 is XX and 6 is VI, giving MMXXVI. The year 1994 is MCMXCIV, which is M (1000) + CM (900) + XC (90) + IV (4). The year examples below the converter can be clicked to load them.