How Roman numerals work
Roman numerals are built from seven letters whose values never change: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500 and M = 1000. You form a number by writing these letters from the largest value to the smallest and adding them up. A letter may be repeated up to three times in a row — III is 3 and XXX is 30 — but never four times, which is where subtractive notation comes in.
Under subtractive notation, a smaller letter placed immediately before a larger one is subtracted instead of added. That turns the awkward four-in-a-row cases into compact pairs: IV = 4, IX = 9, XL = 40, XC = 90, CD = 400 and CM = 900. To build any number, handle the thousands, then the hundreds, then the tens, then the ones, picking the right symbol or subtractive pair for each place.
| Symbol / numeral | Value | Note |
|---|---|---|
| I | 1 | Base unit |
| V | 5 | Five |
| X | 10 | Ten |
| L | 50 | Fifty |
| C | 100 | One hundred |
| D | 500 | Five hundred |
| M | 1000 | One thousand |
| IV | 4 | Subtractive: 5 − 1 |
| XL | 40 | Subtractive: 50 − 10 |
| XC | 90 | Subtractive: 100 − 10 |
| MMXXIV | 2024 | MM + XX + IV |
Reference note: this converter uses standard rules for the range 1–3,999 and does not use the bar (vinculum) notation for larger values. Roman numerals have no symbol for zero and represent only positive whole numbers.
Frequently asked questions
- How do I write a number in Roman numerals?
- Break the number into thousands, hundreds, tens and ones, then write each part using the largest letters first. Use subtractive pairs like IV and IX for fours and nines.
- What is 2026 in Roman numerals?
- 2026 is MMXXVI — that is MM (2000) + XX (20) + VI (6).
- How does subtractive notation work (IV, IX)?
- A smaller letter before a larger one is subtracted from it, so IV is 5 − 1 = 4 and IX is 10 − 1 = 9. The same gives XL = 40, XC = 90, CD = 400 and CM = 900.
- What is the largest standard Roman numeral?
- With standard rules the largest is 3,999, written MMMCMXCIX. Values above that need a bar over letters to multiply by 1,000, which this tool does not use.
- Is there a zero in Roman numerals?
- No. The system has no symbol for zero and represents only positive whole numbers from 1 upward.
- How do I read a Roman numeral?
- Read left to right and add each letter's value, but subtract when a smaller letter sits just before a larger one. So XLIX is (50 − 10) + (10 − 1) = 49.