About the Roman Numeral Converter
This converts between ordinary numbers and Roman numerals in both directions. People use it to read a date or copyright year written in Roman numerals (like a film's MMXXIV), to number book chapters, clock faces, monarchs and events, or for tattoos and inscriptions where a year is written the classical way. Switch direction, type a value, and it converts as you go, checking that Roman numerals are properly formed.
How it works
Number → Roman builds the numeral greedily from the largest symbol down, using the standard subtractive pairs (CM, CD, XC, XL, IX, IV) so it never writes four of a symbol in a row. Roman → Number reads the letters and adds their values, subtracting a symbol when a smaller one precedes a larger (as in IV = 4). It also round-trips the result to catch malformed numerals — if converting the number back doesn't reproduce exactly what you typed, it flags the numeral as invalid (so IIII or VX are rejected).
Assumptions and behaviour
- The letter values are I=1, V=5, X=10, L=50, C=100, D=500, M=1000.
- Uses the standard subtractive notation (IV not IIII, IX not VIIII).
- Roman input is case-insensitive; blank space is ignored.
- Invalid input is flagged rather than silently producing a wrong answer.
Limitations
- Range is 1 to 3999. Classic Roman numerals have no zero and no simple way to write numbers above 3999 (that needs overlines or bracket notation for thousands, which this tool doesn't produce). There's also no numeral for zero or negatives.
- No fractions. The Romans used a separate duodecimal fraction system (unciae), which isn't covered.
- It enforces standard, well-formed numerals, so non-standard historical variants may be reported as invalid.
Privacy
The conversion runs entirely in your browser. Nothing is uploaded or stored.
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