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Roman Numeral Converter
Convert a number (1–3999) to a Roman numeral or a Roman numeral back to a number, with strict validation — malformed forms like IIII, VV, or IC are rejected rather than silently misread.
Examples
| Number | Roman |
|---|---|
| 1 | I |
| 4 | IV |
| 9 | IX |
| 40 | XL |
| 90 | XC |
| 400 | CD |
| 900 | CM |
| 2024 | MMXXIV |
| 3999 | MMMCMXCIX |
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Features
- Converts both directions: number to Roman numeral, and Roman numeral to number
- Strict validation — rejects malformed forms like IIII, VV, or IC
- Covers the full standard range, 1 to 3999
- Copy the result with one click
How to use
- Choose a direction.
- Enter a number or a Roman numeral.
- The converted result appears automatically, or a specific error if the input isn’t valid.
FAQ
- Why is the range limited to 1–3999?
- Standard Roman numerals — the ones built from I, V, X, L, C, D, and M without any special notation — can represent any number from 1 to 3999. Numbers beyond that need a non-standard extension (like a bar over a symbol to multiply it by 1000), and there's no single agreed convention for that, so this tool sticks to the range everyone recognizes.
- Why does it reject things like IIII or IC?
- Those aren't valid Roman numerals under the standard rules, even though a naive parser could assign them a number. A symbol can repeat at most 3 times (so 4 is IV, never IIII), and subtraction is only allowed for specific pairs (IV, IX, XL, XC, CD, CM) — you can't subtract I from C (IC) or L from C (LC isn't subtractive either). This tool validates the canonical form rather than guessing at malformed input.
- Is input sent anywhere?
- No — both directions are computed entirely in your browser.