Roman Numeral Converter
How Roman Numerals Work
Roman Numerals are an additive (and subtractive) numbering system used in ancient Rome. While we use the Hindu-Arabic system (0-9) today, Roman numerals are still used for movie copyrights, Super Bowl numbers, and clocks.
The system uses seven basic letters to represent values:
| Symbol | Value | Mnemonic |
|---|---|---|
| I | 1 | (I = 1 finger) |
| V | 5 | (V shape of hand) |
| X | 10 | (X = two Vs) |
| L | 50 | - |
| C | 100 | (Centum - Century) |
| D | 500 | - |
| M | 1,000 | (Mille - Millennium) |
The Subtraction Rule (IV vs IIII)
Roman numerals are usually written from largest to smallest (left to right) and added together.
- VI = 5 + 1 = 6
- CX = 100 + 10 = 110
However, to avoid four identical letters in a row (like IIII or XXXX), we use subtraction.
The Rule: If a smaller letter is placed before a larger letter, you subtract it.
- IV: 5 - 1 = 4
- IX: 10 - 1 = 9
- XC: 100 - 10 = 90
- CM: 1000 - 100 = 900
Have you ever noticed that old clocks often use IIII instead of IV for the number 4? This is a tradition known as the "Watchmaker's Four." It is done for visual symmetry opposite the VIII (8) on the other side of the dial.
How to Convert Large Years (Like 2025)
To convert a year like 2025 into Roman numerals, you must break it down by place value (Thousands, Hundreds, Tens, Ones).
- 2000 = MM (1000 + 1000)
- 000 = (Skipped)
- 20 = XX (10 + 10)
- 5 = V
Combine them: MMXXV.
What about 1999?
1000 (M) + 900 (CM) + 90 (XC) + 9 (IX) = MCMXCIX.
Why is there no Zero?
The Romans did not have a number for Zero. They didn't see "nothing" as a value that needed to be counted. The concept of Zero as a number was developed later in India (which is why our modern system is called Hindu-Arabic).
Common Uses Today
Why do we still learn this ancient system?
- Copyright Dates: Look at the end credits of a movie (e.g., MCMLXXXIV for 1984).
- Super Bowl: The NFL uses Roman Numerals to give the game a sense of grandeur (e.g., Super Bowl LVIII).
- Monarchs: Kings and Queens use them (Queen Elizabeth II).
- Chemistry: Oxidation states (Iron(III) oxide).