Roman Numeral Converter

Convert numbers to Roman numerals and back.

Number or Roman Numeral

Number → Roman

MMXXIV

How Roman numerals work

Roman numerals combine seven letters — I (1), V (5), X (10), L (50), C (100), D (500), and M (1000). Symbols are added when written largest-to-smallest, and subtracted when a smaller symbol precedes a larger one (IV = 4, IX = 9, CM = 900). The standard system represents 1 through 3999. This converter auto-detects whether you typed a number or a numeral, and validates that numerals are well-formed before converting — all in your browser.

Built and maintained by Meet Shah · Last updated 19 July 2026

What this tool is used for

Reading a date or a chapter number written in Roman numerals.
Producing a numeral for a title, a preface page or an outline level.
Checking a numeral is well formed before using it.
Converting a film or monument inscription date.
Working out a numeral for a clock face or a document section.

Frequently Asked Questions

What are the subtractive rules?: Only six subtractive pairs are valid: IV, IX, XL, XC, CD, CM. Only I, X and C may subtract, and only from the next two higher symbols — so IL for 49 is invalid; it is XLIX.
What is the largest number expressible?: 3,999 (MMMCMXCIX) in standard notation, because M cannot repeat more than three times. Larger values needed a vinculum — an overbar multiplying by 1,000 — which has no plain-text representation.
Why is there no zero?: Because the system is additive and evolved for counting and tallying, where nothing needs no symbol. Positional notation requires a zero placeholder; Roman numerals do not, which is also why arithmetic with them is so awkward.
Why do clock faces use IIII instead of IV?: A genuine convention, not an error. IIII balances VIII visually across the dial, and one story attributes it to avoiding IV as the initial letters of IVPITER. Clockmakers have used it since long before standardisation.
Are lowercase numerals valid?: They are widely used for book front-matter page numbers and outline lists, though the classical form is uppercase. Converters should accept both on input and let you choose the output case.
Are there invalid numerals that still parse?: Yes — `IIII`, `VV` and `IC` all decode to a number under a permissive parser while violating the standard rules. Strict validation and lenient parsing give different answers, and which you want depends on whether you are reading or writing.
How are years commonly written?: Additively and at length — 1998 is `MCMXCVIII`. That is why film credits and cornerstones can run to a dozen characters, and why the subtractive rules matter: the naive form would be longer still.

Common errors and gotchas

Writing a subtractive pair that is not permitted, such as IL for 49 instead of XLIX.
Repeating a symbol more than three times, which the standard form does not allow.
Expecting a zero or a negative, which the system has no representation for.
Converting a very large number, where the standard notation runs out above a few thousand.
Confusing the letter I with the digit 1, which matters when transcribing from an inscription.