Digital Conversion
Convert a whole number to a standard Roman numeral, or read a canonical Roman numeral as a number. Invalid sequences and values outside 1–3999 are clearly rejected.
Standard modern notation only: 1–3999, subtractive pairs IV, IX, XL, XC, CD, and CM. Noncanonical forms are rejected.
Modern standard Roman numerals use I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1000. In additive notation, values are summed from left to right: VIII is 5 + 1 + 1 + 1 = 8. Thousands can begin with up to three Ms in this tool, so MMM represents 3000.
Six subtractive pairs shorten particular values: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, and CM = 900. This is why 944 is CMXLIV rather than DCCCCXXXXIIII. The converter builds numerals from largest standard value down to smallest and checks the reverse input against that canonical rendering.
The reverse converter does not simply add any combination of letters. Forms such as IC for 99, VX for 5, or IIII for 4 are rejected because they are not canonical under the modern convention used here. MMXXVI is 2000 + 20 + 6 = 2026. Case is normalized, but spaces inside a numeral and unrelated letters are invalid.
Classical usage varied across time and place, and inscriptions sometimes use forms such as IIII. This tool intentionally applies a single modern scheme suitable for ordinary dates, headings, and educational exercises. It does not support zero, negative numbers, fractions, overbars for thousands, or values above 3999.
| Example | Result | Why it matters |
|---|---|---|
| 4 | IV | I before V is one of the six accepted subtractive pairs. |
| 49 | XLIX | Forty and nine each use their own subtractive pair. |
| 944 | CMXLIV | Hundreds, tens, and ones are converted separately. |
| 3999 | MMMCMXCIX | The highest supported value stays within standard unbarred notation. |
Check a modern Roman numeral year on a title page, plaque, or film credit.
Translate a numbered section heading without hand-counting repeated symbols.
Compare additive and subtractive patterns with immediate validation.
Historical inscriptions can use nonstandard spellings. A rejected historical form is not necessarily a transcription error; it is outside this modern scheme.
MMXXVI: MM is 2000, XX is 20, and VI is 6.
The converter requires the canonical modern form IV for 4, although IIII can occur in historical contexts and on clocks.
Not in the standard notation supported here. The allowed range begins at 1.
Ordinary unbarred modern notation has no universally simple form beyond MMMCMXCIX; larger values often need an overbar or another convention.
Last reviewed: October 26, 2026. This tool runs in your browser. Verify important data against its source format and encoding.
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