Roman Numeral Converter

About the Roman Numeral Converter

Type a number to get its Roman numeral, or a Roman numeral to get its value — the direction is detected as you type, so 1994 gives MCMXCIV and MCMXCIV gives 1,994. Standard numerals cover 1 to 3,999; from 4,000 to 3,999,999 the thousands are written with a bar over them (the vinculum, which multiplies by 1,000), so 4,000 is I̅V̅ and 1,000,000 is M̅.

Every numeral you type is checked against the standard rules of subtractive notation. If it breaks one — IIII, IC, VX, IIX — the page says which rule, reads it the usual way and shows the standard form. Each answer is broken into its symbols and values, dates can be converted (day, month and year separately), and the reference chart below is generated by the same code as the converter.

Common uses

• Writing a year, a chapter or a page number in Roman numerals, or checking one before it is printed or engraved.
• Turning a birthday or wedding date into numerals for an invitation, a card or a tattoo — and checking each part before it is permanent.
• Reading numerals on buildings, film credits, clock faces, monarchs’ names and book prefaces.
• Homework on place value and Roman numerals, with every step explained.

The rules of standard Roman numerals

• Seven symbols: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1,000.
• Symbols are written from the largest to the smallest and added: MDCLXVI = 1,000 + 500 + 100 + 50 + 10 + 5 + 1 = 1,666.
• A smaller symbol written before a larger one is subtracted, but only in six pairs: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). So 49 is XLIX, not IL, and 99 is XCIX, not IC.
• I, X, C and M may be repeated up to three times in a row; V, L and D are never repeated and never subtracted.
• Only one symbol is subtracted at a time (8 is VIII, not IIX), and after a pair such as IX the next symbol must be smaller than I — which is why each digit of the number is written separately: 1994 = M | CM | XC | IV.
• There is no zero, no negative number and no decimal point.

Numbers above 3,999: the vinculum

A bar over a numeral multiplies it by 1,000: V̅ = 5,000, X̅ = 10,000, L̅ = 50,000, C̅ = 100,000, D̅ = 500,000 and M̅ = 1,000,000. This tool writes the number of thousands with a bar and the rest normally, so 12,345 = X̅I̅I̅CCCXLV and 3,999,999 = M̅M̅M̅C̅M̅X̅C̅I̅X̅CMXCIX.

Conventions for large numbers were never fixed. Some writers keep M for one to three of the thousands (X̅MM for 12,000); the converter reads that and marks it as a correct older style. The old apostrophus characters in Unicode — ↀ (1,000), ↁ (5,000), ↂ (10,000), ↇ (50,000) and ↈ (100,000) — are read too.

Unicode Roman numeral characters

Unicode has separate characters for Roman numerals in its Number Forms block (U+2150–U+218F): Ⅰ Ⅴ Ⅹ Ⅼ Ⅽ Ⅾ Ⅿ from U+2160, lower-case ⅰ ⅴ ⅹ ⅼ ⅽ ⅾ ⅿ from U+2170, and single characters for 1 to 12 such as Ⅻ. They were added for compatibility with East Asian standards, and the Unicode Standard (section 22.3) says that for most purposes it is preferable to write Roman numerals with ordinary Latin letters — they are easier to search, copy and read aloud. The converter reads both and offers the Unicode form only as an extra.

Limitations

• The range is 1 to 3,999,999. Roman fractions (a separate system in twelfths) and the larger historical notations, such as a frame around a numeral for ×100,000, are not converted.
• Old inscriptions often use non-standard forms such as IIII, IIX for 8 or XIIX for 18. The tool reads them the usual way — a symbol before a larger one is subtracted — and marks them as not standard, so IIX reads as 10; the writer may have meant 8.
• Copied numerals with a bar use the combining overline character (U+0305). Most fonts draw it well, but some apps place it slightly off; the ASCII form with underscores (_V) is offered for those.

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