Roman Numeral to Number Converter
Type a number in one box or a numeral in the other and the other side follows. The breakdown shows which symbol contributed what, and the tool says whether what you typed is in the standard form or just something a reader would understand.
How it breaks down
| Piece | Value | Why | Running total |
|---|
The seven symbols
| Symbol | Value | May be placed before |
|---|---|---|
| I | 1 | V and X |
| V | 5 | nothing |
| X | 10 | L and C |
| L | 50 | nothing |
| C | 100 | D and M |
| D | 500 | nothing |
| M | 1000 | nothing |
The seven symbols, and the rule that trips people up
Roman numerals use I, V, X, L, C, D and M for 1, 5, 10, 50, 100, 500 and 1000. Symbols are written largest first and added together, so MDCLXVI is 1666 and uses each symbol exactly once.
The complication is subtractive notation, where a smaller symbol in front of a larger one is subtracted: IV is 4, IX is 9, XL is 40. The rule that surprises people is that this does not apply to any pair you like. Only I, X and C can be subtracted, and only from the next two symbols up. So I goes before V and X, X goes before L and C, C goes before D and M. Nothing else.
That is why 99 is XCIX and not IC. IC looks like it should work — 100 minus 1 — but V, L and D are never subtracted, and a symbol can never be subtracted from something more than ten times its size. The tool above will still read IC as 99, because a human would, and will tell you the standard form is XCIX.
Why clocks say IIII
Look at a traditional clock face and four is almost always IIII, not IV. Watchmakers have an old habit of calling this the "regulator" style, and several explanations circulate: that IIII balances the visually heavy VIII opposite it, that it lets a dial be cast from three moulds of IIII, VVIIIIII and XXXXIIIIII, or that a French king objected to IV. None of them is documented well enough to be called the reason.
What is true is that IIII was perfectly ordinary in Roman inscriptions, and that the strict subtractive rules we now treat as standard were tightened up long after Rome. The tool accepts IIII and tells you it is readable but non-standard, which is exactly its status.
What Roman numerals cannot do
- Zero. There is no symbol for it. The system counts things, and the Romans had no need to write down a quantity of nothing in a numeral.
- Negative numbers. Same reason.
- Fractions, in the way you would expect. Romans did use fractions, in twelfths, with their own symbols: S for a half and dots for each additional twelfth. They are not part of the numeral system most people mean.
- Large numbers, comfortably. Three M characters take you to 3000, and MMMCMXCIX is 3999. Above that the classic convention is a vinculum, a bar over a symbol multiplying it by a thousand, so a barred V is 5000. A bar is a typographic mark rather than a character, which makes it awkward in plain text, and there was never one agreed way to write it. This tool stops at 3999 for that reason.
Where you still meet them
Years on buildings, monuments and film copyright notices. Regnal numbers and popes. Book preface page numbers. Chemical group numbers and some musical chord notation. Super Bowls, famously, until Super Bowl 50 — the NFL used the digits rather than write L on the logo, then went back to numerals the following year.
The year use is the most common reason people come to a converter. 2026 is MMXXVI: two thousands, two tens, a five and a one. Years starting with 19 tend to be long, because 1900 is MCM and the hundreds column gets expensive.
Where this tool falls short
The parser is deliberately permissive. It walks left to right and subtracts any symbol smaller than the one after it, which is how a human reads a numeral, so it will happily return a number for input that no Roman ever wrote. Type IIXX and it returns 20, when the writer may have meant 18. Genuinely ambiguous input gets a number rather than an error, plus a warning that the form is not standard. Read the warning.
It also does not handle the vinculum, the medieval apostrophus notation that wrote large numbers with reversed C symbols, or numerals embedded in running text. Paste a whole sentence and it will reject the letters that are not numeral symbols rather than try to find the numeral inside it.
Frequently asked questions
What year is MMXXVI?
2026. MM is two thousand, XX is twenty, V is five and I is one. Years are the most common place Roman numerals still turn up, mainly on buildings and in film credits.
Why is 4 written IIII on clock faces?
Tradition, not arithmetic. IIII was normal in Roman inscriptions and clockmakers kept it, probably because it balances the VIII on the opposite side of the dial. IV is the standard form today and both are read as four.
Why is 99 XCIX and not IC?
Only I, X and C can be subtracted, and only from the next two symbols above them. I can precede V and X, so IC is not allowed. Ninety is XC and nine is IX, which gives XCIX.
How do you write numbers above 3999?
With a vinculum, a bar over a symbol that multiplies it by a thousand, so a barred V is 5000. It is a typographic convention rather than a character, was never standardised, and is not supported here. The limit is MMMCMXCIX, which is 3999.
Is there a Roman numeral for zero?
No. The system has no symbol for nothing and no way to express it. Medieval scribes writing in Latin used the word nulla when they needed to, but that is a word, not a numeral.
Last updated September 19, 2026