Roman Numeral Converter
Convert whole numbers to Roman numerals and back.
Results update as you type.
About this calculator
A Roman numeral converter turns an ordinary number from 1 to 3,999 into Roman numerals like MCMLXXXIV, or reads a Roman numeral back into a number. Romans built values from the seven symbols I, V, X, L, C, D and M — worth 1, 5, 10, 50, 100, 500 and 1,000.
The system is mostly additive, writing larger symbols before smaller ones and adding them up, but it uses a subtractive shortcut for the 4s and 9s: IV is 4, IX is 9, XL is 40 and CM is 900. This converter also validates the input, rejecting malformed numerals such as IIII or VX.
Worked example: 2024 breaks into 1000 + 1000 + 10 + 10 + 4, which is MM + XX + IV = MMXXIV. Reading it back, MMXXIV adds 1000 + 1000 + 10 + 10 + (5 − 1) = 2024. Because the symbols only reach M, the largest value the standard system can write is 3,999, or MMMCMXCIX.
Frequently asked questions
How does the subtractive rule work?
When a smaller symbol comes before a larger one it is subtracted: IV is 4 (5 − 1), IX is 9, XL is 40 and CM is 900. Otherwise symbols are added left to right.
Why is the maximum 3,999?
Standard Roman numerals only go up to 3,999 (MMMCMXCIX). Representing 4,000 or more needs an overline notation that most fonts and forms cannot show.
Is there a zero in Roman numerals?
No. The Roman system has no symbol for zero and no place value, which is one reason it was eventually replaced by Arabic numerals for arithmetic.
How do I write 4 and 9 in Roman numerals?
They use the subtractive rule: 4 is IV (one before five) and 9 is IX (one before ten). The same pattern gives 40 = XL, 90 = XC, 400 = CD and 900 = CM.
What number is the Roman numeral MMXXIV?
MMXXIV is 2024: two Ms are 2,000, two Xs are 20, and IV is 4. This Roman numeral converter reads each symbol left to right, subtracting when a smaller one precedes a larger one.
Why does the converter reject numerals like IIII?
Standard Roman notation never repeats a symbol four times; four is written IV, not IIII. The converter checks that a numeral is in canonical form and flags non-standard spellings as invalid.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/roman-numerals/curl
curl "https://calculator.free/api/v1/roman-numerals/?amount=2024&from=arabic&to=roman"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/roman-numerals/?" + new URLSearchParams({
"amount": "2024",
"from": "arabic",
"to": "roman"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.