What range of numbers can I convert?

Standard Roman numerals cover 1 to 3999. There is no symbol for zero or negative numbers, and values above 3999 require overline notation that is not part of the classic system.

How does it validate Roman numerals?

After decoding, the tool re-encodes the result and checks it matches your input. This rejects malformed sequences like IIII or VX that decode to a number but are not valid Roman numerals.

Is anything sent to a server?

No. Both conversions run entirely in your browser — nothing is uploaded.

What do the seven Roman numeral symbols mean?

I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. Numbers are built by combining these, using subtraction for 4 (IV), 9 (IX), 40 (XL), 90 (XC), 400 (CD) and 900 (CM).

How do I write the year 2026 in Roman numerals?

2026 is MMXXVI — M (1000) + M (1000) + X (10) + X (10) + V (5) + I (1). Years are a common use, for example on film credits, monuments and clock faces.

Why is 4 written IV and not IIII?

Standard Roman numerals never repeat a symbol four times. Instead a smaller symbol before a larger one means subtraction, so 4 is IV (5 − 1) and 9 is IX (10 − 1). This tool rejects IIII because it re-encodes the decoded value and checks it matches.

Can it convert numbers above 3999?

No. The classic system stops at 3999 (MMMCMXCIX). Larger numbers need an overline (vinculum) to multiply a symbol by 1000, which is not part of standard ASCII Roman numerals.

Roman Numeral Converter

Roman numeral converter — both directions

This tool converts any whole number from 1 to 3999 into a Roman numeral, and decodes a Roman numeral back into a number. It is handy for writing years on documents, reading clock faces and monument inscriptions, numbering book chapters or appendices, and checking homework. Decoding uses strict validation, so it tells you when a sequence is not a legal numeral.

How it works

To encode, the tool walks a fixed table from the largest value down — 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) — appending each symbol while it still fits and subtracting its value. This is why 1994 becomes MCMXCIV, not MIM. To decode, it adds each symbol’s value but subtracts when a smaller symbol precedes a larger one (IV = 5 − 1). It then re-encodes the result and rejects the input if the two do not match, catching malformed strings like IIII or VX.

Example

Enter 2026 → MMXXVI. Decode MCMXCIV → 1994. Try IIII and it is flagged as invalid because the correct form is IV.

Number	Roman
4	IV
9	IX
40	XL
90	XC
2026	MMXXVI
3999	MMMCMXCIX

Both directions run entirely in your browser — nothing is uploaded.