Roman Numeral Converter

How to convert Roman numerals

1. Type a whole number (such as 2026) or a Roman numeral (such as MCMXCIV) in the box. The tool detects which one it is and converts as you type.
2. Read the result, then click Copy to copy the Roman numeral or the number.
3. Check the Steps list: it shows how the number breaks down, or how each symbol adds or subtracts.
4. For numbers above 3,999, tick Allow numbers above 3,999 (vinculum: a bar multiplies by 1,000).

Lowercase numerals (mcmxciv) and the Unicode numeral characters such as Ⅻ are accepted too. The Examples buttons fill in a year, a Roman numeral and a non-standard form to try.

The seven symbols

Symbols are written from largest to smallest and added up: MDCLXVI = 1,000 + 500 + 100 + 50 + 10 + 5 + 1 = 1,666. To avoid four identical symbols in a row, six subtractive pairs place a smaller symbol before a larger one: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900).

To write a number, take each decimal place in turn. 1994 = 1,000 + 900 + 90 + 4 = M + CM + XC + IV = MCMXCIV. The largest standard numeral is 3,999, MMMCMXCIX, because M may only be repeated three times.

Standard form and why IIII or VX are flagged

When you enter a numeral, this tool reads it the lenient way (a symbol, or a run of the same symbol, placed before a larger one is subtracted) and then compares it with the standard form. If they differ, you get the value it most likely means, the standard spelling, and the rule that was broken:

• I, X and C are repeated at most three times. IIII reads as 4 but is written IV. Clock faces are the famous exception: many show IIII, a tradition kept for visual balance.
• V, L and D are never repeated, because VV is simply X, LL is C and DD is M.
• Only I, X and C are subtracted, and only from the next two larger symbols. IV, IX, XL, XC, CD and CM are the only pairs. So VX (5) is written V, IL (49) is XLIX, IC (99) is XCIX, and XM (990) is CMXC.
• Order matters: IIX is not a standard way to write 8 (VIII), even though some old inscriptions use it.

These rules are the modern convention used in publishing, for movie copyright years, monarchs, chapters and outlines. The Romans themselves were less strict, and you will find non-standard forms on real monuments.

Large numbers: the vinculum

With the vinculum option, a bar over a numeral multiplies it by 1,000. This tool writes the thousands under the bar and the rest below 1,000 without it: 4,000 = I̅V̅, 12,345 = X̅I̅I̅CCCXLV, 1,000,000 = M̅, up to 3,999,999. The bar is a combining overline (U+0305) placed over each letter; you can also paste letters with a macron. Other historical conventions exist, such as a box around the numeral for hundreds of thousands, or the apostrophus (CIↃ for 1,000), so large numbers can look different elsewhere.