Roman Numeral Converter
Convert between Arabic numbers and Roman numerals in either direction - just type either one and it auto-detects.
MCMXCIV
Recommended Settings
Pro Tips
- •Roman numerals can only represent whole numbers from 1 to 3999 - there's no standard symbol for zero or numbers beyond MMMCMXCIX
- •The tool automatically detects whether you typed a number or Roman numeral, so you can convert in either direction from the same box
- •Subtractive notation (like IV for 4, or CM for 900) is handled automatically according to standard Roman numeral rules
- •An invalid Roman numeral sequence (like IIII or VX) is flagged rather than silently converted, since these violate standard formation rules
Most Popular
Most people convert a birth year or copyright year into Roman numerals, or decode one seen on a movie credit or clock face
When to Use This Tool
Decode a Roman numeral copyright year like MCMXCIV seen in film credits.
Understand Roman numeral markings on a traditional clock or watch face.
See exactly how subtractive notation and symbol combination rules work.
Get the correct Roman numeral for a sequel number, chapter, or edition.
How It Works
Detect whether your input is a plain number or a sequence of Roman numeral letters
For numbers, greedily subtract the largest matching numeral value (including subtractive pairs like CM and IV) until reaching zero
For Roman numerals, sum values left to right, subtracting a value that precedes a larger one, then verify it round-trips back to the same numeral
100% Private
Files never leave your device. All processing happens locally in your browser.
Lightning Fast
Powered by Client-side Roman numeral algorithm for optimal performance on modern browsers.
Open Source
Built with verified, open-source libraries. Fully transparent.
Frequently Asked Questions
What's the largest number Roman numerals can represent?
Using standard notation, 3999 (MMMCMXCIX) is the largest value, since there's no standard single symbol for 5000 or higher without additional notation like a bar over a numeral.
Why does IIII sometimes appear instead of IV on clocks?
IIII is a traditional stylistic variant occasionally used on clock faces for visual symmetry, but IV is the standard subtractive form used everywhere else, including by this tool.
Can Roman numerals represent zero or negative numbers?
No, the classical Roman numeral system has no symbol for zero and cannot represent negative numbers.
How do I know if my Roman numeral is valid?
This tool checks that your input round-trips correctly - if converting it to a number and back produces the exact same numeral, it's valid; otherwise it's flagged as invalid.