Roman Numeral Converter

About Roman Numeral Converter

Convert Arabic numbers to Roman numerals and back. Values from 1 to 3,999 use the notation taught today (MMXXVI and so on); values from 4,000 to 3,999,999 use a bar over the letters, the vinculum, which multiplies them by 1,000.

When reading Roman numerals, the tool accepts only the standard form. IIII, VV or IC are rejected even though you can guess what they mean. That the standard itself is a convention settled long after Rome is the point that confuses people most, so it is where this page starts.

The subtractive rule was not always the rule

Writing a smaller letter before a larger one to subtract it (IV = 4, IX = 9, XL = 40, CM = 900) existed in Roman times, but it was never used consistently. Inscriptions and manuscripts often write 4 as IIII and 9 as VIIII, sometimes mixing both styles in one text. The tidy rule taught in schools today was settled through medieval and early-modern printing and teaching, not by the Romans.

The rules this tool enforces are the modern ones. Following them, every number from 1 to 3,999 has exactly one spelling:

• I may be subtracted only from V and X, X only from L and C, and C only from D and M. So 99 is XCIX, not IC, and 999 is CMXCIX, not IM.
• V, L and D are never subtracted and never repeated (X, not VV).
• No letter appears more than three times in a row (IV, not IIII).

Why the standard stops at 3,999, and what the bar does

The largest basic letter is M for 1,000. With the three-in-a-row limit, MMMCMXCIX = 3,999 is as high as the standard notation goes. MMMM breaks the rule, and there is no standard letter for 5,000.

For larger numbers, Roman and medieval writers drew a line over letters. V̄ meant 5,000, X̄ 10,000, M̄ 1,000,000. This tool builds values of 4,000 and above by putting a bar over the thousands group and appending the remaining 0 to 999 in plain letters. So 4,000 becomes I̅V̅ and 1,234,567 becomes M̅C̅C̅X̅X̅X̅I̅V̅DLXVII. The bar is the Unicode combining overline (U+0305), so it may sit slightly off in some fonts, and pasted text must include that combining character to be recognized.

Historically there were other schemes too, such as framing a numeral on three sides to multiply by 100,000, and none became universal. The tool does not go beyond 3,999,999.

The IIII on clock faces

Many Roman-numeral clock dials show four o'clock as IIII rather than IV. Explanations offered include visual balance with the VIII opposite, avoiding the first letters of IVPPITER (Jupiter in Latin inscriptions), and more economical casting of the numerals. None of these is established. What is certain is that IIII is not a mistake: it is an old and legitimate form. The tool rejects it as non-standard input, but on a clock or an old inscription, read it as 4.

Where you actually meet Roman numerals

Copyright years at the end of film credits (MCMXCIX = 1999), cornerstones, front-matter page numbers in books (lowercase i, ii, iii), Super Bowl numbers, the names of popes and monarchs (Elizabeth II, Benedict XVI), outline headings and watch dials. Almost all of them fall inside 1 to 3,999. Input is case-insensitive, so lowercase xiv reads as 14.

The tool can also copy results as the dedicated Unicode Roman numeral characters (Ⅿ, Ⅾ, Ⅽ and so on). Those look tidy but are separate code points: search engines, screen readers and spell checkers may not treat them as the letters M, D, C, so plain letters are usually the safer choice in running text.

Worked examples

How to use it

1. Choose the direction: number to Roman, or Roman to number.
2. Enter the value; lowercase Roman letters are fine.
3. Copy the result, optionally as Unicode Roman numeral characters.

Frequently asked questions