Roman Numeral Converter

Convert numbers to Roman numerals and Roman numerals back to numbers — live, both ways, across the classic 1 to 3999 range. Everything runs in your browser; your data is never sent anywhere and nothing is stored.

How to use the Roman numeral converter

  1. Type a whole number from 1 to 3999 in the top field — the Roman numeral appears instantly below.
  2. Or type a Roman numeral (upper or lower case) in the bottom field — the number appears instantly above.
  3. Use the Copy button on either field to grab the result.

The converter uses standard subtractive notation: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). The seven symbols are I=1, V=5, X=10, L=50, C=100, D=500 and M=1000.

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Frequently asked questions

What range of numbers can I convert?

Standard Roman numerals cover the whole numbers from 1 to 3999. There is no symbol for zero and no standard single-symbol way to write 4000 or more, so this converter accepts integers in the 1–3999 range. Anything outside that range is rejected with a short message.

What is subtractive notation?

Instead of writing four of the same symbol, Roman numerals place a smaller symbol before a larger one to mean "subtract". That gives the six subtractive pairs IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). This converter always uses this standard form.

Is the Roman numeral input case-sensitive?

No. You can type mcmxciv, MCMXCIV or any mix of cases — the converter reads it the same way and shows the value 1994. The result is always displayed in uppercase, which is the conventional form.

Why does it say my Roman numeral is invalid?

The input must be a well-formed Roman numeral: symbols in descending value order, no symbol repeated more than three times, and only the six valid subtractive pairs. Strings like IIII, VV or IC are rejected because they are not standard notation.

Is my data sent anywhere?

No. Both conversions run entirely in your browser — nothing is uploaded to a server and nothing is stored. The tool works offline once the page has loaded.

What are the Roman numeral symbols?

There are seven: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. Every number from 1 to 3999 is written by combining these with the subtractive rule.