Roman Numeral Converter
Type a number or a Roman numeral into either box. The other side updates as you type, and invalid numerals are flagged with the reason.
How Roman numerals work
Seven letters carry fixed values — I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000 — and you add them left to right. The one twist is subtractive notation: when a smaller value sits immediately before a larger one, it is subtracted instead. So IV is 4 (5 − 1) and XC is 90 (100 − 10). Only six subtractive pairs are valid: IV, IX, XL, XC, CD and CM. The system has no zero and no way to write fractions, which is why it was replaced for arithmetic.
The rules that make a numeral valid
- I, X, C and M may repeat up to three times in a row. IIII is not standard; IV is.
- V, L and D never repeat. VV would be X, so it is simply written as X.
- Only I, X and C are subtracted, and only from the next two values up. IX and IV are valid; IL and IC are not.
- Subtract only from the next two denominations. XC (90) is valid; XM would not be — 990 is CMXC.
- Read left to right, largest first, apart from the six subtractive pairs.
This is why 1999 is MCMXCIX and not MIM: each part of the number is expressed separately as 1000 + 900 + 90 + 9.
Roman numeral chart
| Number | Roman | Number | Roman |
|---|---|---|---|
| 1 | I | 30 | XXX |
| 2 | II | 40 | XL |
| 3 | III | 50 | L |
| 4 | IV | 90 | XC |
| 5 | V | 100 | C |
| 6 | VI | 400 | CD |
| 9 | IX | 500 | D |
| 10 | X | 900 | CM |
| 14 | XIV | 1000 | M |
| 20 | XX | 2026 | MMXXVI |
Why the limit is 3,999
M is the largest single letter, and it may repeat at most three times, so MMMCMXCIX — 3,999 — is the largest number standard notation can express.
The Romans handled larger figures with a vinculum, a bar drawn over a numeral to multiply it by a thousand: V̄ meant 5,000 and X̄ meant 10,000. Because that is a typographic mark rather than a letter, it is rarely supported, and most converters — this one included — stop at 3,999.
How to use the Roman Numeral Converter
- Type a number between 1 and 3,999 into the left box.
- Or type a Roman numeral into the right box to decode it.
- Malformed numerals are explained rather than silently accepted.
Frequently asked questions
What is XIV in numbers?
14. The X is 10, and IV is 4 because the I before the V subtracts one from five.
Why is 4 written IV and not IIII?
Standard notation uses subtraction to avoid four identical letters in a row. IIII does appear historically, most famously on clock faces, where it is still used for visual balance against the VIII opposite.
Is there a zero in Roman numerals?
No. The system has no symbol for zero and no concept of place value, which is precisely why positional Hindu-Arabic numerals replaced it for calculation.
What is the largest Roman numeral?
MMMCMXCIX, which is 3,999, in standard notation. Larger values needed an overbar to multiply by a thousand.
How do I write the current year?
2026 is MMXXVI — two thousands, two tens, a five and a one.
Related tools
Last reviewed September 4, 2026. Results are estimates for general information only.