DIY Cost Tools

Roman Numeral Converter

Convert a whole number to Roman numerals, or read a Roman numeral as a decimal number. Enter either format in the same field. The converter checks standard modern subtractive notation and shows a place-value breakdown so you can see how the result is built.

How to convert in either direction

Enter a whole number using ordinary digits, or enter Roman letters I, V, X, L, C, D and M.
Select Convert numeral, or press Enter. The input type is detected automatically.
Read both representations and the breakdown. Invalid input hides the old result and explains the accepted notation.

The tool is useful for reading dates on buildings, interpreting numbered chapters, checking movie-year numerals and preparing simple educational examples. Confirm the original lettering when reading a weathered inscription: a missing stroke can change the value.

Symbols and subtractive notation

The supported symbols have these values:

Roman numeral symbol values
Symbol	Value	Symbol	Value
I	1	V	5
X	10	L	50
C	100	D	500
M	1,000	—	—

Standard modern notation uses six subtractive pairs: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900. Other supported combinations add their values. For example, VI = 5 + 1 = 6. A smaller letter before a larger one is not automatically valid: IL is rejected; forty-nine is XLIX.

Conversion method

For number-to-Roman conversion, select the largest available symbol or subtractive pair that fits the remaining value, append it and subtract its value. Repeat until the remainder is zero. The ordered values are 1,000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4 and 1.

For Roman-to-number conversion, first validate the numeral’s thousands, hundreds, tens and ones groups. Within each valid group, add symbols unless a smaller symbol appears immediately before a larger symbol; in that case subtract the smaller value. Finally, convert the total back to standard Roman form and require an exact match. That check prevents malformed strings from producing a plausible but misleading answer.

Worked example: 2026 to MMXXVI

Split 2026 into 2,000 + 20 + 6. The groups are MM, XX and VI, giving MMXXVI. Reading that numeral back gives 1,000 + 1,000 + 10 + 10 + 5 + 1 = 2026. These are the default inputs and results.

For a subtractive example, 944 splits into 900 + 40 + 4, or CM + XL + IV = CMXLIV. The converter also accepts cmxliv and displays the normalized uppercase result.

Scope and limitations

This converter supports whole numbers 1–3,999 in standard modern notation using ordinary Latin letters. It rejects zero, negatives, fractions, overbar notation and historical or clock-face variants such as IIII. The 3,999 ceiling is this tool’s supported range, not a claim that Roman numeral systems can never represent larger values.

Historical usage varied. A clock or inscription may legitimately use a form outside the modern convention implemented here. Use a relevant historical reference when interpreting those forms. Do not use this converter alone to settle a disputed historical date or the meaning of a damaged inscription. Leading zeros in decimal input are allowed and removed from the displayed number; internal spaces and punctuation are rejected.

Frequently asked questions

Why is IIII rejected if it appears on clocks?

The converter validates modern subtractive notation, where four is IV. Clock-face and historical variants require a different set of conventions, so this tool reports them as outside its scope.

How do I convert a number above 3,999?

This tool does not support those values. Larger-number conventions can use additional marks such as overbars; choose a converter that explicitly supports the convention you need.

Can Roman numerals represent zero here?

No. The supported I-through-M notation has no zero symbol, and this converter only accepts positive whole numbers.

Why does IC not convert to 99?

IC is outside the accepted subtractive pairs. Standard modern ninety-nine is XCIX: ninety (XC) plus nine (IX).

Does uppercase matter?

No. Ordinary lowercase Roman letters are accepted and normalized to uppercase. Special single-character Unicode numerals are not accepted; type their equivalent Latin letters.

Review notes and reference

Reviewed October 3, 2026. Conversion was checked in both directions for every supported integer from 1 through 3,999, including each subtractive pair. The default and 944 worked examples, lowercase input, blank input, out-of-range values and malformed numerals were checked. Wolfram MathWorld’s Roman Numerals reference documents the symbol values, subtractive examples and historical variants. The rules and supported range above define this converter’s behavior.