Roman Numeral Converter
Convert numbers to Roman numerals and Roman numerals back to numbers.
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Roman numerals both ways
This Roman numeral converter works in two directions: turn a number from 1 to 3999 into standard Roman numerals, or decode a Roman numeral back into a number. Switch mode with the selector and the tool validates your input as you type.
How Roman numerals work
The symbols are I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Smaller values before a
larger one are subtracted (IV = 4, IX = 9), which is why the classic range stops at 3999 without
extra notation.
How to use the Roman Numeral Converter
- Choose a mode. Select number-to-Roman or Roman-to-number.
- Enter your value. Type a number (1–3999) or a Roman numeral.
- Read the conversion. See the converted result appear instantly.
- Check validity. Invalid entries are flagged so you can correct them.
Frequently asked questions
Why is the maximum 3999?
Standard Roman numerals use M for 1000 and have no single symbol beyond it, so 3999 (MMMCMXCIX) is the largest value written without special overline notation.
How is a Roman numeral validated?
The tool decodes the numeral and then re-encodes it; if the result does not match your input exactly, the numeral is not in valid canonical form.
Is it case sensitive?
No. Lower-case Roman numerals are accepted and treated the same as upper-case.
Is my data stored?
No. Conversions run entirely in your browser and nothing is sent to a server.