Why is the range limited to 1 to 3999?

Standard Roman numerals only use the letters I, V, X, L, C, D and M. The largest value expressible without overlines or other extensions is 3999 (MMMCMXCIX). Zero and negative numbers have no Roman representation.

What is the subtractive rule?

A smaller numeral placed before a larger one is subtracted: IV is 4 and IX is 9. Only I, X and C may be used subtractively, and only before the next one or two larger symbols, which is why 4 is IV and never IIII in standard form.

Does the parser reject invalid numerals?

Yes. It rejects strings that do not round-trip, such as IIII, VX or IC. A valid numeral must re-encode to exactly the same text, so malformed input is flagged rather than silently accepted.

How do I write a year like 1999?

1999 is MCMXCIX: M is 1000, CM is 900, XC is 90 and IX is 9. The tool builds this automatically by repeatedly subtracting the largest possible value-symbol pair.

Are lowercase Roman numerals supported?

Yes. The parser uppercases your input before reading it, so mcmxcix and MCMXCIX both decode to 1999. Output is always uppercase, the conventional form.

What is the Roman Numeral Converter?

Convert any integer from 1 to 3999 into standard Roman numeral notation, and parse Roman numerals back into integers with strict subtractive-rule validation. Runs entirely in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Roman Numeral Converter

Name: Roman Numeral Converter
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Roman numerals encode numbers with seven letters — I, V, X, L, C, D, M — using addition and a limited subtractive rule. This converter turns any integer from 1 to 3999 into a correctly-formed numeral and parses numerals back to integers, rejecting malformed input.

How it works

Encoding uses a greedy table of value-symbol pairs, including the subtractive pairs, processed from largest to smallest:

1000 M   900 CM   500 D   400 CD
 100 C    90 XC    50 L    40 XL
  10 X     9 IX     5 V     4 IV
   1 I

For each pair, the algorithm appends the symbol while the remaining value is greater than or equal to that pair’s value, then subtracts it. Decoding scans the string left to right: if a symbol’s value is less than the next symbol’s value it is subtracted, otherwise it is added. To validate, the decoded integer is re-encoded and compared to the original text — anything that does not match exactly (such as IIII or IC) is reported as invalid.

Worked examples

The year 2024 becomes MMXXIV: two M’s for 2000, XX for 20, and IV for 4. The subtractive rule is strict — 99 is XCIX (90 + 9), never IC, because a smaller symbol may only precede the next one or two steps up in value. A few illustrative conversions:

Integer	Roman numeral	Notes
4	IV	Not IIII
14	XIV	X + IV
44	XLIV	XL + IV
99	XCIX	XC + IX (not IC)
2024	MMXXIV	MM + XX + IV
3999	MMMCMXCIX	Maximum value

Where Roman numerals are still used

The converter is useful for a surprising range of practical needs:

Clock faces — most Roman-numeral clocks use IIII for 4 (not IV) by historical convention, though IV appears on some; the validator flags IIII as non-standard
Film and TV copyright dates — studios have required Roman copyright years in credits, making 2024 → MMXXIV a common real-world conversion
Book front matter — preface and introduction pages are typically numbered in lowercase Roman numerals (i, ii, iii, iv…)
Monarchs and popes — Elizabeth II, Pope John XXIII, and similar regnal names
Super Bowl and Olympic numbering — Super Bowl LVIII, the XXXIII Olympiad

The converter handles all of these cases. Lowercase input (mcmxcix) is accepted and uppercased automatically; output is always uppercase per the standard convention.