Roman to Decimal
Valid range: I to MMMCMXCIX (1-3999)
Invalid Roman numeral format!
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Decimal to Roman
Valid range: 1 to 3999
Please enter a number between 1 and 3999.
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Educational Guide to Roman Numerals
Basic Roman Numeral Symbols
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1000 |
Roman Numeral Rules
Symbols are typically written from largest to smallest, from left to right. Their values are added together.
Example: VI = 5 + 1 = 6
Example: MMXXIII = 1000 + 1000 + 10 + 10 + 1 + 1 + 1 = 2023
When a smaller symbol appears before a larger symbol, the smaller value is subtracted from the larger.
Example: IV = 5 - 1 = 4
Example: CM = 1000 - 100 = 900
Only certain combinations use this principle:
- IV = 4 (not IIII)
- IX = 9 (not VIIII)
- XL = 40 (not XXXX)
- XC = 90 (not LXXXX)
- CD = 400 (not CCCC)
- CM = 900 (not DCCCC)
Symbols I, X, C, and M can be repeated up to three times in succession.
Example: III = 3
Example: XXX = 30
Symbols V, L, and D cannot be repeated.
Invalid: VV (should be X)
| Number | Roman Numeral | Pattern |
|---|---|---|
| 4 | IV | 1 before 5 |
| 9 | IX | 1 before 10 |
| 40 | XL | 10 before 50 |
| 90 | XC | 10 before 100 |
| 400 | CD | 100 before 500 |
| 900 | CM | 100 before 1000 |
Practice Quiz
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