Roman Numeral Converter

Write numbers as Roman numerals and read them back

Roman Numeral Converter turns a whole number from 1 to 3,999 into its standard Roman form, and reads a Roman numeral back into an ordinary number. There are two linked boxes: type in either one and the other fills in as you go.

Roman input is checked strictly against the standard form, so a numeral that merely “adds up” isn’t passed as correct. When a spelling isn’t standard, the tool explains which rule it breaks and, where the letters can still be read, offers the correct version. All of this runs in your browser.

How to convert to and from Roman numerals

1. To get a Roman numeral, type a number from 1 to 3,999 into Number. Thousands separators such as 1,994 are fine.
2. To read a numeral, type it into Roman numeral. Upper or lower case both work; the result is shown in capitals.
3. Check the breakdown under the result to see how each part of the numeral maps to thousands, hundreds, tens and ones.
4. If a numeral isn’t standard, read the message under the box. When a “Did you mean” line appears, press Use it to swap in the standard form.
5. Use Copy numeral or Copy number to copy either side.

Reading the result and the breakdown

The result line shows both forms, such as MCMXCIV = 1,994. The breakdown splits the number by decimal place and shows the Roman letters for each: 1,994 = M (1,000) + CM (900) + XC (90) + IV (4). Places that are zero, like the tens in 2008, are simply left out.

Where Roman numerals still appear

• Dates: copyright years at the end of films and TV programmes, foundation stones and inscriptions.
• Events and titles: numbered events, monarchs and popes, sequels and editions.
• Clock faces and outlines: hour markers, chapter numbers and the numbering of document sections or prefaces.
• Design and tattoos: checking a date before it is engraved, printed or inked, when a mistake is hard to undo.

The rules behind standard Roman numerals

Seven letters carry the values: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1,000. Standard numerals follow a few rules, and this converter checks every one.

Adding and subtracting letters

Letters are written from largest to smallest and added up: VIII is 5 + 1 + 1 + 1 = 8. To avoid four of the same letter in a row, a smaller letter placed before a larger one is subtracted instead. Only six such pairs are standard: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900).

Why IIII, VV and IC are rejected

I, X, C and M can appear at most three times in a row, so 4 is IV rather than IIII. V, L and D are never repeated, because two of them make the next letter up: VV is just X. I can only be subtracted from V and X, X only from L and C, and C only from D and M, so 99 is XCIX rather than IC. And only one letter can be subtracted at a time, which rules out IIX for 8 — the standard form is VIII.

For a readable non-standard form, the suggested fix is the standard numeral for the value its letters give under the usual reading, where any letter placed before a larger one is subtracted. IIII reads as 4, so the suggestion is IV.

Limits: no zero, no fractions, nothing above 3,999

The Roman system has no symbol for zero and no negative numbers, and this tool doesn’t handle the Roman twelfths used for fractions. Without repeating M four times, the largest standard numeral is MMMCMXCIX (3,999). Larger values were written with a bar over a letter to multiply it by 1,000 (overline notation), which isn’t supported here.

Roman Numeral Converter: common questions