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Roman Numeral Converter

Convert numbers to Roman numerals and back.

Free online Roman numeral converter

Convert numbers to Roman numerals and Roman numerals back to numbers with this instant, two-way translator. Type a whole number from 1 to 3999 into the Number field, or a numeral into the Roman numeral field, and the other side updates live. It's handy for reading clock faces and book chapters, writing dates on certificates and buildings, decoding movie copyright years, and any time you meet those familiar letters — I, V, X, L, C, D, and M — and need a plain number.

How to convert Roman numerals

  1. To turn a number into a numeral, type it into the Number field (1–3999).
  2. To turn a numeral into a number, type it into the Roman numeral field — lowercase is fine.
  3. Read the converted value instantly on the opposite side.
  4. Click Copy next to either field to send its value to your clipboard.

How Roman numerals are built

Roman numerals use seven letters with fixed values: I=1, V=5, X=10, L=50, C=100, D=500, and M=1000. Numbers are written largest-first and added together, except in subtractive pairs where a smaller symbol sits before a larger one to mean subtraction — IV is 4, IX is 9, XL is 40, and CM is 900. Because a symbol can't repeat more than three times, this tool re-encodes whatever you type and compares it, rejecting malformed numerals like "IIII" or "VV".

Explore more converters

Roman numerals are just one way of writing numbers. If you work with computing radixes instead, our number base converter switches between binary, octal, decimal, and hexadecimal. And when you're drafting the text those numbers appear in, the word counter keeps your writing within length limits. Everything runs in your browser — private, instant, and free.

Frequently asked questions

How does the Roman numeral converter work?

Type a whole number into the Number field or a numeral into the Roman numeral field, and the other side updates instantly. Numbers are encoded using the standard descending value table (M, CM, D, CD, C, and so on), and numerals are decoded with subtractive notation. Everything runs in your browser — nothing is sent to a server.

What numbers can I convert to Roman numerals?

The classic Roman system only represents whole numbers from 1 to 3999. There is no Roman symbol for zero and no standard way to write numbers of 4000 or more without special overline notation, so values outside 1–3999 show an inline error.

Why is my Roman numeral marked invalid?

Roman numerals follow strict rules: you cannot repeat a symbol more than three times in a row (so "IIII" is wrong, it should be "IV"), and symbols like V, L, and D are never repeated. The tool decodes your input, re-encodes it, and checks the two match — if they do not, the numeral is not well formed.

Is the Roman numeral field case sensitive?

No. You can type in lowercase, uppercase, or a mix — for example "mcmxciv" or "McmXciv" — and it is automatically uppercased before conversion. Only the letters I, V, X, L, C, D, and M are allowed.

Is my data private?

Yes. All conversion happens locally in your browser with JavaScript. No numbers or numerals are uploaded, logged, or stored, so the tool is completely private and free to use with no sign-up.

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