Why is the range limited to 1–3999?

Standard Roman numerals only define symbols up to M (1000), and repeating M more than three times isn't valid subtractive notation, so 3999 (MMMCMXCIX) is the largest number the classic letter set can represent.

Can I type lowercase Roman numerals?

Yes, lowercase input like "mcmxciv" is uppercased automatically before parsing, so you don't need to hold shift, though the field displays and copies the result in uppercase.

Why does IIII show as an invalid numeral?

IIII is not standard subtractive notation, the correct form for 4 is IV, and this tool rejects any numeral that doesn't round-trip back to the same string when it's regenerated from its numeric value.

Does it handle zero or negative numbers?

No, Roman numerals have no symbol for zero and no notion of a negative sign, so entering 0 or a negative number returns the error that the value falls outside the 1–3999 range.

Roman Numeral Converter

Convert between integers (1–3999) and Roman numerals, locally.

Local, Runs entirely in your browser, your data never leaves your device.

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Convert between numbers and Roman numerals

This converter works in both directions at once: type a whole number in the top field and its Roman numeral appears below, or type a numeral in the bottom field and its numeric value appears above. It uses standard subtractive notation, the same rules behind clock faces and copyright years, so IV means 4 and CM means 900 rather than IIII or DCCCC. Both fields update locally as you type, and there's a copy button next to the numeral.

How to use the Roman Numeral Converter

Type a whole number from 1 to 3999 into the Number field to see its Roman numeral below.
Or type a Roman numeral, using only the letters M D C L X V I, into the numeral field.
Read the converted value update in the other field as you edit either one.
Copy the Roman numeral with the button next to its input field.

The number-to-numeral direction validates by round-tripping the result: it converts your typed numeral back to a number and re-renders it, so a malformed input like IIII or VX is rejected as "not a valid Roman numeral" rather than silently misparsed.

The supported range is 1 to 3999, because the standard letters M D C L X V I have no way to represent zero or numbers of 4000 and above without non-standard notation like an overline.

Frequently asked questions

Why is the range limited to 1–3999?: Standard Roman numerals only define symbols up to M (1000), and repeating M more than three times isn't valid subtractive notation, so 3999 (MMMCMXCIX) is the largest number the classic letter set can represent.
Can I type lowercase Roman numerals?: Yes, lowercase input like "mcmxciv" is uppercased automatically before parsing, so you don't need to hold shift, though the field displays and copies the result in uppercase.
Why does IIII show as an invalid numeral?: IIII is not standard subtractive notation, the correct form for 4 is IV, and this tool rejects any numeral that doesn't round-trip back to the same string when it's regenerated from its numeric value.
Does it handle zero or negative numbers?: No, Roman numerals have no symbol for zero and no notion of a negative sign, so entering 0 or a negative number returns the error that the value falls outside the 1–3999 range.