The 7 Basic Symbols
Roman numerals use seven letters from the Latin alphabet. Every other value is built by combining these seven.
| Symbol | Value | Memory hook |
|---|---|---|
| I | 1 | One finger |
| V | 5 | A hand spread out (V shape) |
| X | 10 | Two hands crossed |
| L | 50 | Half of 100 (C) |
| C | 100 | Centum — Latin for hundred |
| D | 500 | Half of M |
| M | 1,000 | Mille — Latin for thousand |
Additive Notation
When symbols appear from largest to smallest (left to right), you simply add them together.
Subtractive Notation
When a smaller symbol appears before a larger one, you subtract the smaller value from the larger. There are exactly six valid subtractive pairs:
| Pair | Calculation | Value |
|---|---|---|
| IV | 5 − 1 | 4 |
| IX | 10 − 1 | 9 |
| XL | 50 − 10 | 40 |
| XC | 100 − 10 | 90 |
| CD | 500 − 100 | 400 |
| CM | 1000 − 100 | 900 |
Only these six pairs are valid. You cannot write IC for 99 — the correct form is XCIX.
The Three Core Rules
- No symbol repeats more than three times in a row. 4 is IV (not IIII). 40 is XL (not XXXX).
- Only I, X, and C can be used subtractively. V, L, and D are never placed before a larger symbol.
- A subtractive symbol can only subtract from the next 10× or 5× value. I can precede V and X only; X can precede L and C only; C can precede D and M only.
How to Read Any Roman Numeral
Scan left to right. At each position, ask: is the current symbol smaller than the one to its right?
- Yes → subtract it from the next symbol and treat the pair as one value.
- No → add it to the running total.
Example — MCMXCIX (1999):
How to Write Any Number in Roman Numerals
Work from the largest symbol down. At each step, use the biggest symbol that fits, write it, and subtract its value. Repeat until you reach zero.
Example — 2024:
Real-World Examples
Roman numerals still appear in everyday life:
- Movie sequels: Rocky II, Star Wars Episode IV, Alien³ (using 3)
- Super Bowl: Super Bowl LVIII (58) in 2024
- Clock faces: XII at the top, VI at the bottom
- Copyright years: © MMXXV = © 2025
- Monarchs: King Charles III, Queen Elizabeth II
- Outlines & lists: Legal documents, academic papers
- Architecture: Cornerstones, monuments, government buildings
- Olympics: The Paris games were the XXXIII Olympiad
Common Mistakes
- IIII instead of IV — Only clock faces sometimes use IIII for stylistic reasons; standard notation uses IV.
- VV instead of X — V cannot be repeated. Two fives must become X.
- IL for 49 — Invalid. I can only subtract from V and X. Correct: XLIX.
- LC for 50 — L is not a subtractive numeral. L alone = 50; LC would be an error.
- Reading right-to-left — Always read left to right. XCIX ≠ XCXI.