🏛️Roman Numeral Converter

Roman numeral converter — how does it work?

Our free Roman numeral converter supports conversion in both directions. Enter any Arabic number from 1 to 3999 and you will get its Roman numeral representation — live, without clicking a button. It also works the other way around: enter a combination of letters I, V, X, L, C, D, M and the tool will return the corresponding Arabic value. Everything runs in the browser; no data is sent to any server.

How does it know if the notation is correct?

The converter validates the notation: after reading the Arabic value, it checks whether converting back to Roman gives exactly the same string of letters. This way the tool rejects non-canonical forms such as IIII (instead of the correct IV) or VV (instead of X), and reports the error with a clear message.

Frequently asked questions

Which numbers can be written in Roman numerals?

The standard Roman numeral system covers numbers from 1 to 3999 (i.e. from I to MMMCMXCIX). Zero and negative numbers are not part of the system.

How does Roman numeral validation work?

After you enter a Roman numeral, the converter converts it to an Arabic number and then checks whether converting back gives exactly the same string. This detects invalid forms such as IIII instead of IV.

Does capitalisation matter in Roman numerals?

No. The converter accepts both uppercase (XIV) and lowercase (xiv) — the result is always displayed in uppercase.

Which letters are used in Roman numerals?

Roman numerals use seven letters: I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Combinations such as IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900) represent subtractive notation.