Roman Numeral Converter
Convert between Arabic numbers and Roman numerals (1–3999), both ways, instantly. Fully offline.
Open Roman Numeral Converter →What is the Roman Numeral Converter?
A free, private converter that translates whole numbers into Roman numerals and back again. Type an Arabic number in one box or a Roman numeral in the other and the two stay in sync live as you type, using standard subtractive notation (IV, IX, XL, XC, CD, CM). It handles the classic range of 1 to 3999 and flags anything out of range or malformed with a clear message. Everything runs in your browser, so nothing you enter is ever sent anywhere and it works offline.
How to use Roman Numeral Converter
- Enter a number — Type a whole number between 1 and 3999 in the Arabic box to see its Roman numeral instantly.
- Or enter a numeral — Type a Roman numeral such as MMXXVI in the Roman box and the matching Arabic number appears automatically.
- Read the result — The other box updates as you type; an inline message appears if the value is out of range or not a valid numeral.
- Copy either value — Use the Copy button beside each box to place that number or numeral on your clipboard.
Frequently asked questions
Why is the range limited to 1–3999?
Standard Roman numerals only go up to 3999 (MMMCMXCIX). There is no widely-agreed symbol for zero or for values of 4000 and above, so the converter keeps to the classic range.
Does it use subtractive notation?
Yes. It produces the compact standard forms such as IV for 4, IX for 9, XL for 40, XC for 90, CD for 400 and CM for 900, rather than additive forms like IIII.
What counts as an invalid numeral?
Anything containing letters other than I, V, X, L, C, D and M, or a form that does not match the canonical spelling — for example IIII, IC or VV — is rejected with a message.
Is my input sent anywhere?
No. All conversion happens locally in your browser, so nothing you type ever leaves your device and the tool works offline.
Tips
- Case does not matter for the Roman box — lowercase letters are read as their uppercase equivalents.
- Clear a box to reset it; emptying one side clears the other so you can start a fresh conversion.
- If a numeral is rejected, check for repeated letters or an invalid subtractive pair like IL or XM.