Roman Numeral Converter

Two-way Roman numeral conversion, instantly

This converter works in both directions at once. Type a number between 1 and 3999 and the Roman numeral appears as you type; type a Roman numeral like MCMXCIV and the decimal value fills in immediately. The results panel also shows a symbol-by-symbol breakdown — for example, 2026 becomes M = 1,000 + M = 1,000 + X = 10 + X = 10 + V = 5 + I = 1 — so you can see exactly how the numeral is built, not just the answer.

Validation is strict but helpful. Standard Roman numerals never repeat I, X, C, or M more than three times in a row, and subtractive pairs are limited to IV, IX, XL, XC, CD, and CM. If you enter something non-standard like IIII or VX, the tool flags it and suggests the correctly formed numeral instead of silently guessing. Everything runs in your browser with plain JavaScript — no server, no account, and nothing you type ever leaves your device.

How to use it

1. To convert a number, type it in the Number box — anything from 1 to 3999.
2. To go the other way, type letters in the Roman numeral box; lowercase is fine and is converted automatically.
3. Read the results: the converted value on top and the full symbol breakdown underneath.
4. Edit either box at any time — the other side and the breakdown update live.

FAQ

Why is the limit 3999?

Standard Roman numerals have no symbol above M (1,000) and allow at most three repeats, so MMMCMXCIX (3,999) is the largest number that can be written normally. Larger values historically used a vinculum (an overline multiplying by 1,000), which is not part of the standard alphabet this tool uses.

Is IIII valid for 4?

Not in standard form — 4 is written IV. IIII does appear on many clock faces by tradition, so the tool recognizes what you meant and suggests the correct numeral.

Is there a symbol for zero?

No. The Roman system has no zero and no negative numbers, which is why the converter starts at 1.

Does it handle lowercase input?

Yes. Type mcmxciv and it is treated as MCMXCIV automatically.