Why is 99 written XCIX rather than IC?

Because only I, X and C may be subtracted, and only from the next two values up. I can precede V and X, but not C. So 99 is ninety (XC) plus nine (IX).

What is the largest number that can be written?

3,999 in the everyday form, which is MMMCMXCIX. Larger values used an overbar to multiply by a thousand, a notation that cannot be typed and is rarely seen outside inscriptions.

Why do clock faces show IIII instead of IV?

A long-standing convention with several competing explanations — visual balance against VIII opposite, casting efficiency, and a superstition about the letters of Jupiter's name among them. None is settled, and the practice persists regardless.

Is there a Roman numeral for zero?

No. The system has no zero, no fractions in the standard form and no negative numbers, which is a large part of why positional notation replaced it for anything requiring arithmetic.

Roman Numeral Converter

Numbers to Roman numerals and back again.

Everything runs inside your browser. Your files never leave your device.

Input

Result

The result appears here as you type.

Ask about Roman Numeral Converter

Questions about what this tool does, which option to pick, or what it can and cannot handle.

The question you type here is sent to an AI provider to be answered — your files and whatever you put in the tool above are not, and the assistant cannot see them. Answers are generated and can be wrong. The tool itself is not guessing: it runs deterministic code on your device.

About the Roman Numeral Converter

Roman numerals turn up on clock faces, in book chapters, on building dedications, in film credits and in monarchs' names. Reading them is a skill that fades quickly without practice, so converting in both directions is a reasonable thing to want.

The system uses seven letters — I, V, X, L, C, D and M — and works by addition, with a subtractive rule for the awkward cases. Placing a smaller value before a larger one subtracts it, which is why IV is four and IX is nine rather than IIII and VIIII.

The subtractive rule has constraints that are frequently broken. Only I, X and C can be subtracted, and only from the next two values up: I from V and X, X from L and C, C from D and M. So 99 is XCIX, not IC, even though IC is shorter and reads plausibly. The strict form is what the calculator produces and what a validator will accept.

The system has no zero and no way to express a fraction or a negative number, which is a serious limitation for arithmetic and the reason Roman numerals were replaced. It also has no standard notation above 3,999 in the everyday form — larger numbers used an overbar to multiply by a thousand, which is impractical to type.

Historical inscriptions do not always follow the strict rules, and clock faces are the famous exception: many use IIII rather than IV for four, a convention with several competing explanations and no settled one. The converter accepts common non-standard forms when reading, and always produces the strict form when writing.

How to use it

1Enter a number to get the numeral, or a numeral to get the number.
2Read the result. The strict subtractive form is used when writing.
3Check that any numeral you are entering follows the rules — only I, X and C may be subtracted.
4Note the 3,999 ceiling: above that the system needs an overbar notation that cannot be typed.

Questions

Why is 99 written XCIX rather than IC?: Because only I, X and C may be subtracted, and only from the next two values up. I can precede V and X, but not C. So 99 is ninety (XC) plus nine (IX).
What is the largest number that can be written?: 3,999 in the everyday form, which is MMMCMXCIX. Larger values used an overbar to multiply by a thousand, a notation that cannot be typed and is rarely seen outside inscriptions.
Why do clock faces show IIII instead of IV?: A long-standing convention with several competing explanations — visual balance against VIII opposite, casting efficiency, and a superstition about the letters of Jupiter's name among them. None is settled, and the practice persists regardless.
Is there a Roman numeral for zero?: No. The system has no zero, no fractions in the standard form and no negative numbers, which is a large part of why positional notation replaced it for anything requiring arithmetic.