How to use the roman numeral converter

1. Type a number from 1 to 3999, such as 2026, to get its Roman numeral.
2. Or type a Roman numeral, such as MCMXCIV, to get the number. Upper and lower case both work.
3. Read the result and the breakdown. The steps show how the value was built from its parts.
4. If your numeral is not valid, read the message. It explains which rule was broken and suggests the standard form when it can.

Formula

A smaller symbol written before a larger one is subtracted. Otherwise symbols are added from left to right.

Worked example

The rules this converter enforces

Standard Roman numerals follow a few fixed rules. The symbols I, X, C and M may repeat up to three times in a row. V, L and D never repeat. A subtraction is written by putting one smaller symbol before a larger one, and only six pairs are allowed: IV, IX, XL, XC, CD and CM. The numeral must run from the largest place value to the smallest, so thousands come first, then hundreds, tens and ones.

Input is checked strictly against these rules, and it also checks the reverse. That means every number has exactly one valid numeral. IIII is rejected because I appears four times, and the standard way to write 4 is IV. VX is rejected because V is never subtracted. IC is rejected because I can be placed only before V or X, and 99 is written XCIX. For 49 the standard form is XLIX, not IL. Many clocks print IIII on their face, which is a traditional style but not the standard form.

Why the range stops at 3999

With only seven symbols and a limit of three repeats, the largest standard numeral is MMMCMXCIX, which is 3999. There is no symbol for zero and no way to write negative numbers or fractions in this system. Historically, Romans sometimes marked a thousand-fold multiple by drawing a bar (a vinculum, or overline) above a numeral, so a barred V meant 5,000. That extension is described here for interest only and this converter does not implement it, so numbers above 3999 are refused with an explanation.

Where Roman numerals are still used

You will meet them on building cornerstones, clock faces, book chapters and prefaces, outlines, movie copyright years, monarch and pope names such as Elizabeth II, and event numbering such as sports finals. Lowercase forms, such as i, ii and iv, are common for page numbers in the front matter of books, which is why the result also shows a lowercase form.

Assumptions and limits

• Only standard subtractive notation is accepted. Older additive forms such as IIII or VIIII are treated as invalid.
• The range is 1 to 3999. Zero, negative numbers, decimals and larger values are refused.
• Digits convert to a numeral and letters convert to a number. Mixed input such as 1V is rejected.
• Only the letters I, V, X, L, C, D and M are recognized. Unicode Roman numeral characters such as the single symbol for twelve are not accepted.
• The overline extension for thousands is not implemented.

Formulas reviewed October 10, 2026. See the calculation methodology for how SumPanda rounds, tests and sources its formulas.

Frequently asked questions