Roman Numeral Converter
Numbers to Roman numerals and back, 1–3999 — with the subtraction rules explained and strict validation both ways.
| Symbol | Value | Subtraction pair | Value |
|---|---|---|---|
| I | 1 | IV / IX | 4 / 9 |
| V | 5 | XL / XC | 40 / 90 |
| X | 10 | CD / CM | 400 / 900 |
| L | 50 | ||
| C | 100 | ||
| D | 500 | ||
| M | 1000 |
How to use this tool
- Type a number (1–3999) or a Roman numeral — the conversion happens as you type, in either direction.
How it works
Seven symbols carry the system: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Values add left to right, except the six subtraction pairs — IV(4), IX(9), XL(40), XC(90), CD(400), CM(900) — where a smaller symbol before a larger one subtracts. Standard notation tops out at 3999 (MMMCMXCIX); the Romans handled larger numbers with an overline bar this notation doesn't include.
Frequently asked questions
What is 2026 in Roman numerals?
MMXXVI — MM (2000) + XX (20) + VI (6).
Why is 4 written IV and not IIII?
Subtractive notation became the standard form — though IIII survives on clock faces by tradition. This converter reads both but always writes the standard form.
Why does it stop at 3999?
Standard notation allows at most three repeats of a symbol, and there's no subtraction pair above CM (900), so 4000 would need MMMM. Romans wrote larger numbers with a vinculum (overline) multiplying by 1,000.