Roman Numeral Converter
Convert numbers to Roman numerals or Roman numerals back to numbers. This tool uses strict modern canonical notation from I to MMMCMXCIX (1–3,999).
Two-way conversion: use the first field for numbers to Roman numerals, or the second field for Roman numerals to numbers.
How Roman numeral conversion works
Modern canonical Roman numerals use the subtractive pairs IV, IX, XL, XC, CD and CM alongside I, V, X, L, C, D and M. The converter returns one modern canonical spelling for each supported value, so an additive form such as IIII is rejected rather than treated as an alternative spelling of IV.
This implementation supports whole numbers from 1 to 3,999. Values above 3,999 require notation conventions outside this tool's deliberately bounded model. For other number and format tools, browse the Numbers & Converter Tools directory.
About this tool
Converts whole numbers from 1 to 3,999 to the common modern subtractive form and rejects non-canonical input such as IIII, VX, IIV or MMMM.
Students, editors and designers who need a consistent modern Roman-numeral form. Historical inscriptions may use valid-looking additive variants that this strict converter intentionally rejects.
All validation and conversion happens locally in your browser.
Convention and sources
The supported convention uses I, V, X, L, C, D and M with the subtractive pairs IV, IX, XL, XC, CD and CM, limited to 1–3,999. Historical practice was not fully standardised. Sources reviewed 23 June 2026: UK National Archives; Unicode Standard, numeral characters.