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Roman Numeral Converter

Two-way converter between ordinary numbers (1–3999) and Roman numerals. Switch direction to spell a number in Roman numerals or decode a Roman numeral back to a number, with strict validation that rejects malformed input like IIII or IC. Runs entirely client-side.

Examples

Input · Uses subtractive notation for 900 (CM) and 90 (XC).
1994
Output
MCMXCIV

How it works

The seven symbols
IVXLCDM
1510501005001000

Symbols are added from largest to smallest, and a smaller symbol placed before a larger one is subtracted. Only six subtracting pairs are allowed: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). So 1994 is M + CM + XC + IV, written MCMXCIV.

Going from Roman to number, the tool accepts only the standard form. IIII, IC and VX are rejected, even though they can be read, because the correct forms are IV, XCIX and V. Lower-case letters are accepted. The range is 1 to 3999: there is no Roman zero, and larger numbers need an overline notation that plain text cannot show.

How to use Roman Numeral Converter

Pick a direction
Choose Number to Roman or Roman to Number using the toggle.
Enter a value
Type a number from 1 to 3999, or a Roman numeral made of I V X L C D M.
Read the conversion
The converted value appears instantly, with invalid input flagged.

Why use this tool

Converts in both directions
Validates Roman numerals and rejects malformed forms
Covers the full standard range of 1 to 3999
Private and offline — no data is uploaded

Frequently asked questions

Standard Roman numerals only represent values from 1 to 3999 without special overline notation, so the tool enforces that range.

Yes. Non-canonical forms such as IIII, VX or IC are rejected because they do not round-trip to a valid numeral.

Found a bug or have an idea?

ToolOrbit is actively developed — feedback directly shapes what gets built next.

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