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Roman Numeral Converter

Converts an integer from 1 to 3999 into standard (subtractive-notation) Roman numerals, or parses a Roman numeral back into a number, and shows the value of each symbol group.

When to use

You need to write a year, chapter or clock number in Roman numerals, or read one such as MCMXCIV.

Do not use when: The number is 0, negative, 4000 or larger, or not an integer (standard Roman numerals cannot express these); for other number systems use base-converter.

Formula

Greedy decomposition using M 1000, CM 900, D 500, CD 400, C 100, XC 90, L 50, XL 40, X 10, IX 9, V 5, IV 4, I 1; parsing accepts only the standard form M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})

Inputs

Parameter	Type	Unit	Required	Description
`mode`	enum: to_roman \| from_roman		yes	Conversion direction.
`value`	string		yes	The integer (1–3999) for to_roman, or the Roman numeral (I, V, X, L, C, D, M; case-insensitive) for from_roman.

Outputs

Output	Type	Description
`roman`	string	The numeral in standard form.
`number`	integer	The decimal value.
`breakdown`	string	Symbol groups with their values, e.g. M (1000) + CM (900) + XC (90) + IV (4).

Example

1994 to Roman: {"mode":"to_roman","value":"1994"} → {"roman":"MCMXCIV","number":1994,"breakdown":"M (1000) + CM (900) + XC (90) + IV (4)"}

MMXXVI to number: {"mode":"from_roman","value":"MMXXVI"} → {"roman":"MMXXVI","number":2026,"breakdown":"M (1000) + M (1000) + X (10) + X (10) + V (5) + I (1)"}

GET https://tttkmbb.com/api/v1/calculate/roman-numeral?mode=to_roman&value=1994

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/roman-numeral (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/roman-numeral · Markdown: https://tttkmbb.com/everyday/roman-numeral.md · JSON definition: https://tttkmbb.com/everyday/roman-numeral.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="roman-numeral"
OpenAPI operationId: convert_roman_numeral
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Roman numerals (Wikipedia) (reference)

FAQ

Why is IIII or VIIII rejected?

The converter accepts only standard subtractive notation (IV, IX, XL, XC, CD, CM). Additive forms such as IIII on clock faces are historical variants and are not parsed.

How are numbers above 3999 written?

With a vinculum (overline) multiplying a group by 1000, e.g. an overlined IV for 4000. This calculator supports 1–3999 only.

Related calculators

Number Base Converter — Convert between binary, octal, decimal and hexadecimal.