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Roman Numeral Converter

Convert between Roman numerals and decimal numbers instantly online. Enter a number (1–3999) to get its Roman numeral, or enter a Roman numeral to get its decimal value. Free and runs in your browser.

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Roman numerals use combinations of the letters I, V, X, L, C, D, and M to represent integers. The system uses subtractive notation — IV means 4 (5 minus 1) and IX means 9 (10 minus 1) — to avoid four consecutive identical symbols. Roman numerals were the standard numerical notation in Western Europe until the 13th century, when Hindu-Arabic numerals gradually replaced them for calculation.

Roman numerals remain in active use today: clock faces, book chapter numbering, movie sequel titles, Super Bowl numbering, copyright years in film credits, monarchs and popes (King Charles III), outline numbering in legal documents, and the volume numbering of academic journals and encyclopedias all use Roman notation by convention.

This tool converts bidirectionally between decimal integers (1–3999) and Roman numeral strings. For decimal-to-Roman conversion it applies the standard subtractive algorithm using the 13-symbol value table. For Roman-to-decimal it parses the string left to right, applying subtraction when a smaller value precedes a larger one, per the standard interpretation rules.

Common Use Cases

Formatting legal document outline numbering

Legal briefs, contracts, and court filings use Roman numerals for top-level section headings (I, II, III) and sometimes for subsections. When assembling a document programmatically or converting a numbered list from a plain-text source, converting the section index to a Roman numeral here produces the correctly formatted heading string.

Generating movie title and sequel metadata

Film databases like IMDB and Letterboxd store titles including their Roman numeral suffixes (e.g., Rocky IV, Star Wars: Episode VI). Data pipelines ingesting movie metadata from APIs that return Arabic numeral sequences must convert to Roman numerals to match the canonical title strings used in catalog searches and display.

Producing academic journal volume citations

Citation styles including Chicago and APA use Roman numerals for journal volume numbers in some publication contexts. When writing a bibliography script that generates citations from a database of articles, converting the volume integer to Roman notation here clarifies the expected output format before implementing the conversion in the citation generation code.

Clock and watchface UI development

Custom clock interfaces, watchface apps for Wear OS or Apple Watch, and decorative time displays often use Roman numerals for hour markers. Converting the integers 1–12 to Roman here provides the exact strings to hard-code or generate dynamically in the rendering logic without implementing the conversion algorithm from scratch.

How to Use the Roman Numeral Converter

  1. Enter a decimal number (1–3999) to convert it to a Roman numeral.
  2. Enter a Roman numeral (e.g. XIV) to convert it to decimal.
  3. The result appears instantly. Click Copy Output to copy it.
  4. Use Load Example to convert 2024 as a sample.

Roman Numeral Reference