Roman Numeral Converter Widget

Add a Roman numeral converter to your history, maths or design page. Type 1994 to get MCMXCIV, or type a numeral to read it - invalid spellings such as IIII or IC are flagged with the standard form suggested.

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<iframe src="https://a2z.tools/embed/w/roman-numeral-converter" title="Roman Numeral Converter by A2Z Tools" width="100%" height="480" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

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How it works

The widget detects which way to convert from what is typed. Numbers are converted greedily from the largest symbol value down, using the six subtractive pairs (CM, CD, XC, XL, IX, IV). Roman input is checked against the standard pattern for 1 to 3999, so repeated or out-of-order symbols are refused rather than guessed, and a table shows how the value is built.

Method

  • Symbols: I 1, V 5, X 10, L 50, C 100, D 500, M 1000
  • Subtractive pairs: IV 4, IX 9, XL 40, XC 90, CD 400, CM 900
  • Valid form: ^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$

Limitations

  • Only the standard subtractive form for 1 to 3999; the vinculum (bar) for thousands, the apostrophus and Roman fractions (uncia) are not supported.
  • Unicode Roman numeral characters such as the single-character Ⅻ are not read; type ordinary letters.
  • Irregular historical spellings (IIII, IIX, XIIX) are flagged rather than accepted.

Where publishers use it

  • History and classics lessons
  • Wedding, tattoo and engraving sites where people want a date in numerals
  • Maths pages on number systems
  • Film, book and event sites that number sequels or anniversaries

Questions

Why does it stop at 3999?

Standard Roman numerals allow at most three Ms. Larger numbers used a bar over a numeral (vinculum) to multiply it by 1000, which is not part of the standard form.

Is IIII wrong? Clocks use it.

Many clock faces use IIII for decorative balance, but the standard form, and what exams expect, is IV. The widget flags IIII and suggests IV.

Is there a Roman numeral for zero?

No. The Romans had no numeral for zero; medieval scholars sometimes wrote N for nulla. The widget explains this if you enter 0.

Does lower case work?

Yes, mcmxciv is read as MCMXCIV.

Cite or recommend this tool

If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.

A2Z Tools Roman Numeral Converter
https://a2z.tools/embed/roman-numeral-converter

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