Roman Numeral Converter

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How it works

Seven symbols do all the work: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Symbols are added left to right — except when a smaller symbol sits immediately before a larger one, which means subtract: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900. Those six subtractive pairs are the only ones allowed.

Building a numeral works greedily from the top: take the largest symbol (or pair) that fits, write it down, subtract, and repeat. 1994 = 1000 (M) + 900 (CM) + 90 (XC) + 4 (IV) = MCMXCIV. The standard form never repeats V, L, or D, and never repeats I, X, C, or M more than three times in a row — which is why 4 is IV and never IIII, and why the largest standard value is 3999 (MMMCMXCIX): a fourth M would break the rule.

Strict validation: when you convert from Roman, this page reads the value and then rebuilds the numeral from that value using the rules above. If the rebuilt form does not match what you typed exactly, the input was not a standard Roman numeral and it is rejected. That is how forms like IIII (should be IV) and IC (should be XCIX — I may only subtract from V and X) get caught rather than quietly accepted.

Frequently asked questions

Why do clock faces show IIII for 4? Many traditional clock dials deliberately use IIII instead of IV — a centuries-old watchmaking custom (balance, tradition, and avoiding IV, the first letters of a Latin spelling of Jupiter, are all offered as reasons). It is a dial convention, not the standard numeral form, so this converter follows the standard and expects IV.

How do you write years, like Super Bowl numbers or movie credits? The same way as any number: split the year into thousands, hundreds, tens, and ones and convert each place. 2026 = 2000 (MM) + 20 (XX) + 6 (VI) = MMXXVI.

What about zero, negatives, or numbers over 3999? Classical Roman numerals have no zero and no negatives. Numbers beyond 3999 were written with a bar over a numeral (vinculum) to multiply it by 1,000 — a notation this standard converter does not use, so the range stays 1 to 3999.