Roman numeral converter, with the invalid forms explained instead of accepted
Turn a number into Roman numerals or read one back, live as you type, anywhere from I to MMMCMXCIX. Input is checked against the subtractive rules rather than merely added up, so IIII and IC are refused with the reason and the correct form — four is IV and ninety-nine is XCIX. Every conversion shows its working, symbol group by symbol group, so you can check the answer instead of trusting it. Nothing is uploaded or saved.
- Nothing is uploaded or saved
- Works offline
Film credits, cornerstones and chapter numbers are where most people meet these. 1666 is MDCLXVI — each of the seven symbols once, largest to smallest.
- MM2,000
- XX20
- V5
- I1
There are seven, and no eighth. Only I, X and C are ever placed before a larger symbol, and only before the next two larger ones — which is the rule IC breaks.
- I1Repeats up to three times. Subtracts from V and X: IV is 4, IX is 9.
- V5Never repeated and never subtracted. Two fives is X, not VV.
- X10Repeats up to three times. Subtracts from L and C: XL is 40, XC is 90.
- L50Never repeated and never subtracted. Two fifties is C.
- C100Repeats up to three times. Subtracts from D and M: CD is 400, CM is 900.
- D500Never repeated and never subtracted. Two five-hundreds is M.
- M1,000Repeats up to three times, which is why 3,999 is the ceiling here.
How it works
- 1
Pick a direction
Number to numeral, or numeral to number. Both run on every keystroke, so you can hold a year from a film credit in one field and watch the value settle as you type the last letter. Nothing is submitted and there is no Convert button.
- 2
Read the working, not just the answer
Underneath the result each symbol group is listed with what it contributes: MCMXCIV breaks into M (1000), CM (900, which is 1000 − 100), XC (90) and IV (4). Roman numerals are read in exactly those chunks, largest first, and seeing the chunks is the difference between copying an answer and being able to produce the next one yourself.
- 3
Start from a year if that is why you came
Most people arrive here holding a year — a copyright line at the end of a film, a date carved into a building, a chapter number in a book. The year buttons jump straight to those: 1994 is MCMXCIV, 2026 is MMXXVI, and 1666 is MDCLXVI, which happens to use each of the seven symbols exactly once in descending order.
- 4
Rejections come with a reason
IIII is not accepted, and the message says four is written IV rather than just calling the input invalid. IC is not accepted either, and the message names the rule it broke: only I, X and C may be subtracted, and only from the next two larger symbols. A converter that silently returns 4 for IIII teaches you something false, which is worse than refusing.
- 5
Know where the tool stops, and why
The ceiling is 3,999. M may be written at most three times, so MMMCMXCIX is the largest value the plain seven-symbol notation reaches. Larger numbers were written with a vinculum — an overline meaning multiply by a thousand — and an overline is a mark drawn above a letter, not a character you can type or paste. Rather than invent a stand-in nobody else would read, this page stops.
Frequently asked questions
Why does this stop at 3,999?
Because no symbol above M exists in the plain notation, and M may appear at most three times in a row. That puts the ceiling at MMMCMXCIX, which is 3,999. Bigger values were written with a vinculum, an overline over a symbol meaning it is multiplied by a thousand, so V with a bar is five thousand. An overline is a mark drawn above a letter rather than a character in its own right, so it cannot survive being copied into a spreadsheet, a filename or a chat message. This page refuses instead of inventing a written form — the same reason it refuses IIII.
Is IIII wrong? I have seen it on a clock face.
You have, and clock faces really do use it — IIII appears on a great many dials where the strict form would be IV. It is a design convention on clocks, not a second correct notation, and the reasons given for it are traditional rather than documented. For anything you are writing down — a date, a chapter, a document reference — the subtractive form is the one to use, and it is the only one this converter will produce or accept. Four is IV.
Which symbols can be subtracted, and from what?
Only I, X and C, and only from the next two larger symbols. I goes before V and X, giving IV (4) and IX (9). X goes before L and C, giving XL (40) and XC (90). C goes before D and M, giving CD (400) and CM (900). That is the complete list — six pairs. V, L and D are never subtracted and never repeated, because two of any of them is simply the next symbol up: VV would be X. This is why IC is not 99. Ninety-nine is XCIX, which is ninety (XC) followed by nine (IX).
How do I read MCMXCIV?
Left to right, in groups, largest first: M is 1,000; CM is 900 because the C sits before a larger M and is taken away from it; XC is 90 for the same reason; IV is 4. Add them and you get 1994. The trick is that a smaller symbol before a larger one always belongs with it as a pair, and a smaller symbol after a larger one is simply added. Paste it into the field above and the breakdown prints those four rows.
Is there a Roman numeral for zero?
No. The seven symbols count things, and none of them holds a place, which is why a zero was never needed and never written. This is also why arithmetic in Roman numerals is so awkward: there are no columns to carry between. Medieval scribes writing in Latin sometimes used the word nulla for nothing, but that is a word rather than a numeral, and this converter will not produce it.
Can Roman numerals write fractions or negative numbers?
Not in the notation this page handles. Roman fractions existed and were duodecimal — counted in twelfths, written with their own marks — and they are a separate system from the seven letters, not an extension of them. Negatives have no representation at all: every symbol adds, and the only subtraction in the notation is the six pairs above, which are a spelling rule rather than arithmetic. So this converter takes whole numbers from 1 to 3,999 and nothing else.
What do the seven letters actually stand for?
The values are certain; the origins of the shapes are not, and it is worth being honest about which is which. What is well established is that by the classical period the seven symbols carried the values shown in the table above. The familiar mnemonic that C is centum and M is mille lines up with the Latin words for hundred and thousand, but the letter shapes are older than that reading and scholars have proposed several accounts of where they came from. This page prints the values, which are checkable, and does not tell an origin story it cannot support.
What is the longest Roman numeral under 4,000?
3,888 — MMMDCCCLXXXVIII, fifteen characters. It is the longest because every place value happens to land on the form that needs the most symbols: three Ms, then DCCC for 800, LXXX for 80 and VIII for 8. Type 3888 above and count them. At the other end, 1,000 is a single M, and 1,666 is MDCLXVI, which uses each symbol exactly once from largest to smallest.
Does anything I type here leave my browser?
No. Both directions are a few dozen lines of JavaScript that this page already loaded, so the conversion happens on your machine with no request of any kind, and it keeps working with the network off. Nothing is written to localStorage either — reload the page and the field is back to its starting value, with no record kept anywhere, including by this site.