What is a Roman Numeral Converter?

A Roman Numeral Converter translates ordinary Arabic numbers (1, 2, 3...) into Roman numerals (I, II, III...) and decodes Roman numerals back into regular numbers. Roman numerals still appear today on clock faces, in book chapter numbering, movie release years, monarch and pope names (e.g., Elizabeth II), and outline lists. Converting between the two systems by hand is easy to get wrong once numbers get larger, so this tool automates it instantly.

Key Features

• Two-Way Conversion: Type a regular number to get its Roman numeral, or type a Roman numeral to get its decimal value — the tool detects which one you entered automatically.
• Standard Subtractive Notation: Uses the conventional subtractive form (e.g., 4 → IV, 9 → IX, 1984 → MCMLXXXIV) rather than the older additive style (IIII).
• Instant Validation: If a Roman numeral string cannot be parsed into a valid number, the tool reports an error instead of returning a wrong value.
• 100% Client-Side: All parsing and conversion logic runs directly in your browser. Nothing you type is sent to a server.

How to Use the Roman Numeral Converter

1. Type a number (e.g., 1984) or a Roman numeral (e.g., MCMLXXXIV) into the input field.
2. Click the Convert button.
3. The converted result appears below the input.

Frequently Asked Questions (FAQ)

What is the largest number this tool can convert?

Standard Roman numerals are conventionally defined for values from 1 to 3,999, using the letters I, V, X, L, C, D, and M. Numbers outside that practical range may produce unusually long or non-standard output.

Does it support lowercase Roman numerals?

Yes. Input is automatically uppercased before parsing, so mcmxcix is treated the same as MCMXCIX.

What happens if I type an invalid Roman numeral?

The tool will show an error message indicating the input isn't a valid Roman numeral, instead of guessing or returning zero.