Roman Numeral Converter
Convert a number (1–3999) to Roman numerals, or a Roman numeral back to a number. Shows the result plus a breakdown of how the numeral decomposes.
Input
Enter any whole number between 1 and 3999 — Roman numerals cannot represent anything larger.
Output
Guides
Convert any number from 1 to 3999 into Roman numerals, or translate a Roman numeral back into an ordinary number. Both directions show a breakdown so you can see exactly how the numeral is built.
How to use it
- Pick a Direction: Number → Roman or Roman → Number.
- Type your value — a whole number between 1 and 3999, or a Roman numeral such as
MCMXCIV. - The Result and the Breakdown update as you type.
Lowercase input is accepted (mcmxciv works); the result is always uppercase.
The seven symbols
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1000 |
Numerals are written largest to smallest and added together: MCCXXXIV is 1000 + 100 + 100 + 10 + 10 + 10 + 4 = 1234.
What is subtractive notation?
When a smaller symbol comes before a larger one, it is subtracted rather than added. That is why 4 is IV (5 − 1) and not IIII, and 9 is IX (10 − 1). Only six subtractive pairs are valid:
IV (4) · IX (9) · XL (40) · XC (90) · CD (400) · CM (900)
So 1994 is MCMXCIV: M (1000) + CM (900) + XC (90) + IV (4). This tool validates Roman input against standard subtractive form, so malformed numerals like IIII, VV or IC are rejected rather than silently mis-converted.
Why is 3999 the maximum?
Because there is no symbol above M (1000), and standard notation never repeats a symbol more than three times. The largest writable number is therefore MMMCMXCIX — 3999. Larger values required an overline (a vinculum) meaning "multiply by 1000", a convention with no single agreed encoding, so it is out of scope here.
Is there a Roman numeral for zero?
No. The Romans had no symbol for zero and no concept of it as a number; the idea reached Europe much later via Indian and Arabic mathematics. Negative numbers and fractions of this kind are likewise unrepresentable, which is why the input starts at 1.
Where are Roman numerals still used?
Clock faces, book chapter and preface numbering, film and game sequels, monarchs and popes (Elizabeth II, Benedict XVI), the Super Bowl, building cornerstones and copyright dates on old broadcasts.
Privacy
The conversion runs entirely in your browser — nothing you type leaves your device.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/roman-numeral-converter \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"mode": "to-roman",
"number": "1234"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `roman-numeral-converter` tool (Roman Numeral Converter) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.