Roman Numeral Converter
Convert numbers to Roman numerals and back (1 to 3999), with strict validation of the canonical form.
How it works
Roman numerals combine seven letters — I (1), V (5), X (10), L (50), C (100), D (500) and M (1000) — additively, with one twist: a smaller value placed before a larger one is subtracted. So IV is 4 (5 − 1), IX is 9, XL is 40, XC is 90, CD is 400 and CM is 900.
Type a number from 1 to 3999 to get its numeral, or type a numeral to get the number. The parser
is strict: it accepts only the canonical subtractive form, so IIII and VX are rejected
rather than guessed at — which makes the tool reliable for checking homework or proofreading.
When to use
Reading movie and video game credits (©MCMXCIV), book chapters and prefaces, clock faces, monarchs and popes (Elizabeth II, Benedict XVI), Super Bowl editions, building cornerstones, and outlines that number sections in Roman style. The reverse direction — number to numeral — is handy for tattoo designs, wedding dates, certificates, and typography work.
Practical examples
Movie copyright year
The credits say MCMXCIV. Typing it returns 1994: M (1000) + CM (900) + XC (90) + IV (4).
A date for an engraving
The year 2026 becomes MMXXVI: MM (2000) + XX (20) + VI (6).
Common mistakes
The subtractive rule only allows specific pairs: I before V or X, X before L or C, C before D or M. Forms like IL for 49 or IC for 99 look plausible but are wrong — 49 is XLIX and 99 is XCIX. This converter enforces those rules, which is why some inputs you may see "in the wild" (like IIII on clock faces, a deliberate stylistic exception) are rejected.
Also remember the system simply has no zero and no standard form above 3999 (larger values historically used an overline, which doesn't survive in plain text). That's why the input range stops there.
Frequently asked questions
Why is 4 written IV and not IIII?
Canonical modern usage applies the subtractive rule, giving IV. IIII appears historically and on many clock faces as a stylistic convention, but IV is the standard form and the one this converter accepts.
Why does the converter stop at 3999?
The largest standard symbol is M (1000), and a symbol repeats at most three times, capping the plain notation at MMMCMXCIX = 3999. Larger numbers used an overline multiplying by 1000, which has no common plain-text representation.
Is there a Roman numeral for zero?
No. The system predates the concept of zero as a numeral; medieval texts occasionally used the word "nulla", but there is no symbol.
Are lowercase numerals valid?
Lowercase (mcmxciv) is a typographic variant often used in book front matter and outlines. The converter accepts lowercase input and treats it as uppercase.