Roman Numeral Converter — Arabic to Roman and Back
Convert between Arabic numbers and Roman numerals instantly. Live two-way binding, 1 to 3999 range, client-side only.
Conversions will appear here as you type.
A two-way converter between Arabic digits and Roman numerals. Edit either field and the other updates live using a lookup-table algorithm. Handles the valid range 1 to 3999, validates unusual strings like IIII or VX, and keeps a session history of your last five conversions.
Roman numerals show up more often than most people expect: movie copyright dates, Super Bowl numbering, clock faces, book chapter headings, monarch regnal numbers, and legal document sections. The system is additive with a subtractive shortcut for the 4s and 9s, so 4 is IV (one before five) and 900 is CM (one hundred before one thousand). Valid symbols are M, D, C, L, X, V, and I, and by modern convention no symbol repeats more than three times in a row.
This converter enforces those rules on the way in and out. Type an Arabic number and the corresponding Roman numeral appears with proper subtractive notation. Type a Roman numeral and the tool validates the string, rejects malformed inputs like IIII or IC, and returns the numeric value. The range is capped at 1 to 3999 because Romans did not have a standard symbol for larger numbers. Common presets cover the current year, 100, 500, 1000, and 2000 for one-click testing.
- 1
Type in either field
Enter an integer on the left or a Roman numeral on the right. The other field updates on every keystroke using a lookup-table algorithm.
- 2
Check validation
Out-of-range numbers or malformed Roman strings show a clear badge explaining the problem. Valid inputs display the equivalence as a confirmation badge.
- 3
Reuse recent conversions
The session history card keeps your last five conversions so you can scan back while working through a list.
Year conversions
Translate a copyright year or regnal date to Roman numerals for a design mockup, tattoo, or anniversary gift.
Student homework
Check answers when studying the numeral system for the first time, including the tricky subtractive pairs.
Document formatting
Generate numerals for outline headings, book preface pages, or legal section labels that follow Roman conventions.
Why is the range capped at 3999?
Classical Roman numerals have no standard symbol above M (1000), so the maximum three Ms gives 3000. Adding the 900 shortcut (CM) plus 99 (XCIX) tops out at 3999. Numbers above that required a bar over the symbol (vinculum), which is rarely used today.
Is IIII valid for 4?
IIII appears on some clock faces for visual symmetry but is not the standard form. The tool treats IV as the only correct representation of 4 and rejects IIII on input.
Does it handle zero or negative numbers?
No. Romans had no symbol for zero, and negatives are outside the system. The converter requires a positive integer between 1 and 3999.
Is my input sent anywhere?
No. Conversion runs entirely in your browser. There is no network request, no logging, and the history card is in-memory only.
How do I convert years like 2026?
Type 2026 in the Arabic field and MMXXVI appears on the right. The current-year preset button fills it in for you.