Roman Numeral Converter
Convert Arabic numbers to Roman numerals and parse Roman numerals back to integers.
This converter runs entirely in your browser. Nothing you type is uploaded anywhere.
How to use this tool
This Roman numeral converter works two ways. Pick a mode with the tabs at the top of the tool box. In "Number to Roman" mode, type any whole number from 1 to 3999 and press Convert to see the standard Roman numeral. In "Roman to Number" mode, type a Roman numeral such as MMXXIV and press Convert to read it back as an integer. Use the Copy result button to put the answer on your clipboard, or Clear to start over. Roman numerals are not case sensitive here, so mcmlxxxiv and MCMLXXXIV give the same result.
How the conversion works
Roman numerals use seven letters whose values are added together from left to right. To keep numbers short, the standard subtractive notation lets a smaller value sit in front of a larger one to mean subtraction. So 4 is written IV (5 minus 1) rather than IIII, and 900 is CM (1000 minus 100). To build a numeral, the tool walks through the value list from largest to smallest and pulls out each symbol as many times as it fits. To read a numeral, it compares each letter with the next: if a letter is smaller than the one after it, that letter is subtracted; otherwise it is added. The supported range is 1 to 3999 because classic Roman numerals have no zero and no single symbol above M, so 3999 (MMMCMXCIX) is the largest value the standard form can express cleanly.
A real example
Take the year 2024. Start with thousands: 2024 contains two 1000s, so write MM, leaving 24. There are no 500s, 100s, or 50s in 24. It contains two 10s, so add XX, leaving 4. Four uses the subtractive pair IV. Put it together and 2024 becomes MMXXIV. Reading it back, M (1000) plus M (1000) plus X (10) plus X (10) plus IV (4) sums to 2024, which confirms the result.
Common questions
What is the largest number this Roman numeral converter supports?
It supports 1 through 3999. Standard Roman numerals have no zero and no built-in symbol for values above 1000 other than repeating M, so 3999 written as MMMCMXCIX is the practical upper limit of the everyday form.
Can I convert Latin numerals to numbers as well?
Yes. Roman numerals are sometimes called Latin numerals. Switch to "Roman to Number" mode, type the numeral, and the tool parses it back into a regular Arabic integer.
Why is 4 written IV instead of IIII?
Standard subtractive notation places a smaller symbol before a larger one to mean subtraction, so 4 is IV (5 minus 1) and 9 is IX (10 minus 1). This keeps numerals shorter. You may see IIII on some clock faces, but the converter uses the standard subtractive form.
Does it handle lowercase Roman numerals?
Yes. Input is not case sensitive, so xiv, XIV, and Xiv are all read as 14. The number-to-Roman output is always shown in uppercase.
Is my data sent to a server?
No. All parsing and converting happens locally in your browser using plain JavaScript. Nothing you enter leaves your device.