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Roman Numeral Converter

Type a number from 1 to 3999 and get the standard subtractive-notation Roman numeral, or type a Roman numeral and get the number back — both fields update live, and an invalid numeral is flagged instead of silently guessed at.

  • Both directions: number to numeral, numeral to number
  • Standard subtractive notation (IV, not IIII)
  • Flags malformed numerals instead of guessing
  • Range 1-3999, the classical Roman system limit
  • Runs fully client-side

Converter

Converted locally, nothing uploaded

How to convert Roman numerals

  1. 01

    Type a number

    Any whole number from 1 to 3999 — the Roman numeral fills in automatically.

  2. 02

    Or type a numeral

    Type Roman numerals directly and the number fills in the other field.

  3. 03

    Check for errors

    A malformed numeral like "IIII" or "VV" is flagged, not silently converted.

Why 1 to 3999 and not further#

The classical Roman numeral system has no standard way to write 4000 or higher without a special notation — a bar (vinculum) over a numeral to multiply it by 1000, which is rarely used and not consistently standardized. Rather than invent a non-standard extension, this tool sticks to the range every reference agrees on: 1 to 3999 (MMMCMXCIX).

Why "IIII" is rejected, not converted#

Standard Roman numerals use subtractive notation: 4 is IV, not IIII, and 9 is IX, not VIIII. Some older clock faces and stylized uses do write IIII, but it is not the standard form this tool follows — reading it back rejects it rather than silently accepting an ambiguous or non-standard input as if it were correct.

Frequently asked questions

Why does 4 convert to IV instead of IIII?

IV is the standard subtractive-notation form. IIII appears on some decorative clock faces, but it is not the standard this converter follows, and reading it back is rejected as invalid.

What is the highest number this supports?

3999 (MMMCMXCIX). The classical Roman system has no standard way to represent 4000 or higher without a non-standard notation.

Is my input sent anywhere?

No. The conversion happens entirely in your browser.

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