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Roman Numeral Converter
Convert numbers to Roman numerals and Roman numerals back to numbers (1–3999). Auto-detects direction, validates the input strictly, and shows a quick reference of the seven Roman symbols.
Roman numeral
MMXXVI
2,026 = MMXXVI
Symbol values
I
1
V
5
X
10
L
50
C
100
D
500
M
1,000
How Roman numerals work
Roman numerals combine seven letters — I, V, X, L, C, D, M — using an additive and subtractive system. Symbols are written from largest to smallest and added together: CLXII is 100 + 50 + 10 + 1 + 1 = 162.
When a smaller symbol appears before a larger one it is subtracted: IV is 4 (5 − 1) and CM is 900 (1000 − 100). Only six subtractive pairs are valid — IV, IX, XL, XC, CD, CM — which is why 4 is IV, never IIII.
Symbol reference
| Symbol | Value | Subtractive pair |
|---|---|---|
| I | 1 | IV = 4, IX = 9 |
| V | 5 | — |
| X | 10 | XL = 40, XC = 90 |
| L | 50 | — |
| C | 100 | CD = 400, CM = 900 |
| D | 500 | — |
| M | 1000 | — |
Rules this converter enforces
- Repetition limit: I, X, C, M repeat at most three times; V, L, D never repeat.
- Valid subtractives only: IV, IX, XL, XC, CD, CM — combinations like IL or IC are rejected.
- Range 1–3999: standard notation has no zero and no single symbol above M, capping the practical range at 3999 (MMMCMXCIX).
Common examples
4
IV
9
IX
14
XIV
40
XL
90
XC
400
CD
900
CM
1994
MCMXCIV
2026
MMXXVI
3888
MMMDCCCLXXXVIII