Roman Numeral Converter

What is a Roman numeral converter?

A Roman numeral converter changes a regular number into Roman numerals and translates Roman numerals back into ordinary numbers. You type a whole number from 1 to 3999 and it returns the Roman form using the seven symbols I, V, X, L, C, D and M, or you paste a numeral such as MCMLXXXIV and it returns the value 1984. It removes the guesswork from reading clock faces, copyright dates, book chapters, Super Bowl titles and monument inscriptions, all of which still use Roman numerals today.

How does the Roman numeral converter work?

Going from a number to Roman numerals, the tool uses the standard greedy method. It repeatedly subtracts the largest Roman value that still fits, writes the matching symbol, and continues with what is left. The values it steps through are:

M = 1000, CM = 900, D = 500, CD = 400, C = 100, XC = 90, L = 50, XL = 40, X = 10, IX = 9, V = 5, IV = 4, I = 1

The six two-letter entries (CM, CD, XC, XL, IX, IV) are the subtractive pairs. They exist because a symbol is never written four times in a row, so 4 is IV (one less than five) rather than IIII, and 900 is CM (one hundred less than a thousand) rather than DCCCC.

Going the other way, from Roman to number, the tool sums the symbol values left to right but subtracts any smaller symbol that precedes a larger one. In MCMLXXXIV the C sits before M, so CM counts as 900 rather than 1100. The converter also validates the input: a malformed numeral such as IIII (which should be IV) or VV is rejected, because each repeatable symbol may appear at most three times and V, L and D never repeat at all.

Examples

Here are three worked conversions that match the tool exactly.

Number to Roman: 2026. Subtract the biggest values that fit. 2026 minus 1000 is 1026 (M), minus 1000 again is 26 (M), then 26 holds two tens (XX) leaving 6, which is V plus I. The result is MMXXVI.

Number to Roman: 49. This is where a subtractive pair matters. 49 is not XXXXIX. The largest fit is XL (40), leaving 9, which is IX. The result is XLIX, and 2024 by the same logic is MMXXIV (MM, then XX, then IV for 4).

Roman to number: MCMLXXXIV. Read it in chunks: M is 1000, CM is 900, L is 50, XXX is 30, and IV is 4. Adding 1000 plus 900 plus 50 plus 30 plus 4 gives 1984. Note that the smaller C before M and the smaller I before V both trigger subtraction.

Roman numeral chart

This reference table shows the seven base symbols and the six subtractive pairs the converter relies on.

Symbol	Value	Type
I	1	Base
IV	4	Subtractive pair
V	5	Base
IX	9	Subtractive pair
X	10	Base
XL	40	Subtractive pair
L	50	Base
XC	90	Subtractive pair
C	100	Base
CD	400	Subtractive pair
D	500	Base
CM	900	Subtractive pair
M	1000	Base

What are Roman numerals used for today?

Although they are no longer used for everyday arithmetic, Roman numerals appear in many familiar places:

• Dates and copyright lines — film and TV credits, building cornerstones and book printings often show the year, so a date in Roman numerals like MMXXVI for 2026 is common.
• Clock and watch faces — many traditional dials run from I to XII (with IIII sometimes used as a stylistic exception on clocks, though it is non-standard).
• Numbered series — monarchs (Henry VIII), Super Bowls, Olympic Games, recurring events and movie sequels.
• Outlines and chapters — book volumes, chapter headings, appendices and the front matter of documents.
• Names and pages — generational suffixes (John Smith III) and lower-case page numbers in prefaces.

When you need to convert physical measurements rather than numerals, the pressure converter handles units like PSI, bar and pascals.

Tips and common mistakes

A few rules keep your numerals correct:

• Never repeat a symbol four times. Write IV not IIII, XL not XXXX, and CD not CCCC. This is the single most common error, and the converter rejects the invalid forms.
• V, L and D never repeat. There is no VV or LL; use X for two Vs and C for two Ls.
• Subtract only the right symbol. I may only precede V and X, X only precedes L and C, and C only precedes D and M. So 99 is XCIX, not IC.
• Read large to small. Symbols normally descend in value from left to right; the only exceptions are the six subtractive pairs.
• Watch the order in dates. MMXXIV is 2024 and MMXXVI is 2026 — the trailing IV versus VI is the whole difference between the two years.

Limitations and notes

This converter works with whole numbers from 1 to 3999 only. Standard Roman numerals have no symbol for zero and no way to write negative numbers, fractions or decimals, so values under 1 or above 3999 are out of range. The 3999 ceiling exists because the largest standard symbol is M (1000), and writing four Ms (MMMM) for 4000 breaks the no-four-repeats rule; larger numbers historically used a vinculum (a bar over a symbol meaning times 1000), which this tool does not implement. The converter also enforces strict, modern numeral rules, so historical or decorative variants such as IIII on a clock face are treated as invalid input. For everyday dates, names, outlines and inscriptions the results are exact.

For more unit and value conversions, try the length converter, weight converter and area converter, or browse the full converters category.