Roman numerals are still found in centuries, royal names, book chapters, the Olympic Games and some clocks, but their rules are not always remembered. Here is the complete guide: symbols, reading rules, reference table, common mistakes and an automatic converter at the end.
The seven basic symbols
| Symbol | Value | Origin |
|---|---|---|
| I | 1 | finger (unus) |
| V | 5 | open hand (quinque) |
| X | 10 | two crossed hands (decem) |
| L | 50 | (quinquaginta) |
| C | 100 | centum |
| D | 500 | (quingenti) |
| M | 1000 | mille |
With these seven symbols you can write any number from 1 to 3999 in classical notation.
The two reading rules
Rule 1 — Addition: when a symbol is followed by one of equal or lesser value, add them. Ex: VI = 6, LX = 60, MC = 1100. Rule 2 — Subtraction: when a symbol is followed by one of greater value, subtract. Ex: IV = 4, XC = 90, CM = 900.
Only six subtractions are valid:
| Subtraction | Value | Subtraction | Value |
|---|---|---|---|
| IV | 4 | XL | 40 |
| IX | 9 | XC | 90 |
| CD | 400 | CM | 900 |
For example, IL for 49 and IC for 99 are wrong; the correct forms are XLIX and XCIX.
Reference table (1–1000)
| Value | Roman | Value | Roman | Value | Roman |
|---|---|---|---|---|---|
| 1 | I | 10 | X | 100 | C |
| 2 | II | 20 | XX | 200 | CC |
| 3 | III | 30 | XXX | 300 | CCC |
| 4 | IV | 40 | XL | 400 | CD |
| 5 | V | 50 | L | 500 | D |
| 6 | VI | 60 | LX | 600 | DC |
| 7 | VII | 70 | LXX | 700 | DCC |
| 8 | VIII | 80 | LXXX | 800 | DCCC |
| 9 | IX | 90 | XC | 900 | CM |
| 10 | X | 100 | C | 1000 | M |
Modern years and dates
| Year | Roman |
|---|---|
| 1987 | MCMLXXXVII |
| 1999 | MCMXCIX |
| 2000 | MM |
| 2015 | MMXV |
| 2024 | MMXXIV |
| 2026 | MMXXVI |
Most common mistakes
- ❌ IIII for 4 → the correct form is IV (IIII only appears on clocks by tradition).
- ❌ VV for 10 → the correct form is X; V, L and D are never repeated.
- ❌ IIIII for 5 → the correct form is V; any symbol is repeated at most three times.
- ❌ IC for 99 → the correct form is XCIX; only the six pairs above are used for subtraction.
How to use the converter
- Enter a decimal number (from 1 to 3999) in the first field and the Roman numeral appears instantly.
- Or type a Roman numeral in the second field and you will see its decimal value.
- Expand the breakdown to see each symbol and its contribution.
💡 Breakdown example: MCMLXXXVII = M + CM + LXXX + VII = 1000 + 900 + 80 + 7 = 1987.
Conclusion
- Seven symbols and two rules (addition and subtraction) are enough to read any Roman numeral.
- Standard maximum: 3999 (
MMMCMXCIX). - Common errors: IIII and VV; use IV and X instead.
- The symbol-by-symbol breakdown is the best way to understand each figure.