Roman Numeral Converter
Convert between numbers and Roman numerals in either direction.
Try an example
MCMXCIV
About this calculator
How This Roman Numeral Converter Works
Choose a direction — number to Roman numeral, or Roman numeral to number — enter a value, and the converter returns the result instantly.
Worked Example
1994 converts to MCMXCIV — built from M (1000) + CM (900) + XC (90) + IV (4), each piece chosen greedily from the largest value that still fits.
How the Conversion Works
Converting to Roman numerals works through a fixed table of values from largest (1000, "M") to smallest (1, "I"), including subtractive pairs (900 "CM", 400 "CD", 90 "XC", 40 "XL", 9 "IX", 4 "IV") — repeatedly subtracting the largest value that still fits and appending its symbol. Converting back reads left to right, adding each symbol's value unless a smaller-value symbol precedes a larger one, in which case it's subtracted instead (this is what makes "IV" mean 4 rather than "one before five" needing separate logic).
Range and Limitations
Standard Roman numerals cover 1 to 3,999 (MMMCMXCIX) — the notation doesn't have a standard way to represent zero or negative numbers, and numbers beyond 3,999 required historical extensions (like a bar over a numeral to multiply by 1,000) that aren't in common use today, so this converter is limited to the standard range.
Worked example
1994 converts to MCMXCIV — built from M (1000) + CM (900) + XC (90) + IV (4).
Frequently asked questions
What's the highest number this can convert?
Standard Roman numerals go up to 3,999 (MMMCMXCIX) — beyond that, historical notation gets inconsistent (some systems used a bar over a numeral to multiply by 1,000), so this calculator caps at the standard range.
Why does my Roman numeral input get rejected?
The converter only accepts well-formed, canonical Roman numerals — non-standard forms like IIII (instead of IV) or VV aren't valid under the standard subtractive notation rules.
Why is 4 written as IV instead of IIII?
Roman numerals use subtractive notation for four of the nine values that would otherwise need 4 repeated symbols (4, 9, 40, 90, 400, 900) — placing a smaller symbol before a larger one means 'subtract,' keeping numerals shorter.