Roman Numeral
Convert between arabic numbers (1–3999) and roman numerals. Decoding rejects non-canonical forms (e.g. IIII) so it doubles as a roman-numeral validator.
About Roman Numeral
Roman Numeral converts arabic numbers from 1 to 3999 into roman numerals and back. Decoding rejects non-canonical forms like IIII, so it doubles as a validator that tells you whether a roman numeral is written correctly. Reach for it when numbering chapters, dating a copyright line, or checking a clock-face or monument inscription. It runs entirely in your browser and returns structured JSON.
- Category
- convert
- Input
- Accepts: */*.
- Output
- Outputs: application/json.
- Cost
- Free, runs in your browser
- Memory
- low
Common uses
- Convert a chapter or appendix number into the correct roman numeral for a manuscript
- Work out the year on a copyright notice or movie credit written in roman numerals
- Validate that a hand-written roman numeral uses canonical form, not IIII or VX
- Number a multi-part outline with roman numerals for the top level
- Decode a roman numeral inscription on a building, clock, or monument
- Check the upper bound by confirming what 3999 looks like before a design uses it
Frequently asked questions
What range of numbers is supported?
Arabic integers from 1 to 3999, which is the standard range expressible with the basic roman numeral letters.
Why does it reject IIII?
IIII is a non-canonical form; the canonical numeral for four is IV. Because decoding rejects these, the tool effectively validates whether a roman numeral is written correctly.
What does the output contain?
A JSON result with the converted value and, for decoding, an indication of whether the input was a valid canonical roman numeral.
Does it run on a server?
No. The conversion is purely local arithmetic in your browser; nothing is uploaded.
Can it convert zero or negative numbers?
No. Roman numerals have no representation for zero or negatives, so inputs must fall within 1 to 3999.
Keywords
- roman
- numeral
- arabic
- convert
- encode
- decode