Roman numeral converter

Convert Roman numerals to numbers and convert numbers to Roman numerals.

Enable JavaScript to use the interactive tool. The guide below explains how it works.

Roman Numeral Converter

What it does

The Roman Numeral Converter is a bidirectional tool that translates Arabic (decimal) numbers into Roman numerals and vice versa. It follows the standard subtractive notation (e.g., 4 is IV, not IIII) and supports values ranging from 1 to 3,999. It provides real-time validation to ensure that any Roman numeral entered is mathematically valid.

Why someone uses it

• Historical Research: Decoding dates on monuments, old books, or movie credits.
• Academic Writing: Correctly numbering outlines, prefaces, or appendices in formal documents.
• Design & Aesthetics: Finding the Roman equivalent for clock faces, tattoos, or jewelry engravings.
• Pop Culture: Determining the edition number for major events like the Super Bowl or the Olympics.

Step-by-step instructions

Convert Arabic to Roman

1. Navigate to the Arabic to Roman card.
2. Enter a whole number between 1 and 3,999.
3. The Roman numeral equivalent will appear instantly in the result area.
4. Click Copy to save the result.

Convert Roman to Arabic

1. Navigate to the Roman to Arabic card.
2. Type or paste a Roman numeral (e.g., MCMXCIV).
3. The decimal value will be displayed instantly.
4. If the input is invalid, an error message will appear, and the result will be hidden.
5. Click Copy to save the result.

Examples

• Arabic 2024: Results in MMXXIV.
• Arabic 99: Results in XCIX.
• Roman MCMLXXXVIII: Results in 1988.
• Roman CDXLIV: Results in 444.

FAQs

• What is the maximum number I can convert? The standard Roman numeral system used here supports numbers up to 3,999. Values above this require special symbols (macrons) that are not part of the standard ASCII set.
• Does it support zero? No. The ancient Romans did not have a symbol for zero.
• Can I use lowercase letters? Yes, the tool accepts both uppercase and lowercase Roman numerals.
• Why is 4 not IIII? While some clock faces use IIII, the standard modern convention is the "subtractive" rule where IV (5-1) is used for 4 and IX (10-1) is used for 9.

Common mistakes

• Invalid Sequences: Entering characters that don't follow the subtractive rules (e.g., IL for 49 instead of XLIX).
• Exceeding the Limit: Trying to convert numbers higher than 3,999 or lower than 1.
• Mixing Symbols: Including non-Roman characters like A, B, or S in the input field.

Use cases

• Genealogy: Reading birth or death years in old records.
• Education: Teaching or learning the rules of Roman numerals.
• Creative Projects: Naming book chapters or movie sequels (e.g., Star Wars Episode IV).

Related tools

• Integer Base Converter: For converting between Binary, Hexadecimal, and Decimal.
• List Converter: Useful if you need to convert a whole column of numbers into Roman numerals.
• Math Evaluator: To perform calculations before converting the final result into a Roman numeral.