Roman Numeral Converter

Convert numbers to Roman numerals (1–3999) and Roman numerals back to numbers.

How do Roman numerals work?

Roman numerals use the letters I (1), V (5), X (10), L (50), C (100), D (500) and M (1,000). Values are added from left to right, except when a smaller numeral comes before a larger one, which subtracts it: IV = 4, IX = 9, XC = 90.

Examples

Number	Roman
4	IV
9	IX
40	XL
1994	MCMXCIV
2026	MMXXVI

Rules

A numeral repeats at most three times in a row (III, not IIII).
Only I, X and C are used to subtract, and only before the next two higher numerals.
Standard notation covers 1 to 3,999; there is no zero.

The converter rejects invalid forms such as IIII or IC and explains why.

Frequently asked questions

Why is 4 written IV and not IIII?

Standard notation uses subtraction; IIII appears on some clock faces but is not standard.

Is there a Roman numeral for zero?

No, the Roman system had no zero.

What is the largest standard Roman numeral?

MMMCMXCIX (3,999).