Roman Numeral Converter

What this generator does

Builds the numeral from largest to smallest with the subtractive pairs in the table, so IIII and VIIII cannot arise, and reads numerals back by comparing each numeral against the one after it.

How to use this tool

1. Type a number to get the numeral, or a numeral to get the number.
2. It works out which you meant from what you type.
3. Numerals run from I to MMMCMXCIX, which is 1 to 3999.
4. A numeral written the wrong way is refused, with the right form given.

Understanding the controls

A number or a numeral

Digits give you the numeral; letters give you the number. Numbers run from 1 to 3999, which is as far as the ordinary numerals reach.

Common use cases

• Reading a date on a building, a film or a monument
• Writing a year in numerals for a title or a plaque
• Numbering chapters, appendices or acts
• Checking a numeral somebody else has written
• Teaching how the subtractive pairs work

How this generator works

Three things are confirmed. The numeral is read back and must give the number it came from. No numeral may appear four times in a row, which is what a missed subtractive pair looks like. And the numeral must be exactly the one the standard form produces — IIII reads as four, but four is written IV, so IIII is refused with the correct form given.

Randomness and fairness

Nothing is random. Each number has exactly one standard numeral, and the same input always gives the same answer.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

• One to 3999. Larger numbers need overlines or other notations that are not standardised in plain text.
• No zero and no fractions, neither of which the system has.
• The modern standard form only; medieval and inscriptional variants such as IIII on clock faces are refused.
• Case is ignored on the way in and capitals are used on the way out.

Privacy and your data

Conversion happens in your browser. Nothing you type is transmitted or stored.