How do Roman numerals work?

Roman numerals use letters to represent values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Letters are generally written from largest to smallest, left to right. When a smaller value precedes a larger one, it is subtracted (e.g. IV=4, IX=9, XL=40, XC=90).

What is the largest number in Roman numerals?

Traditional Roman numerals can represent up to 3,999 (MMMCMXCIX). Numbers above 3,999 require a bar over letters to indicate multiplication by 1,000, which this converter does not support.

Is 'IIII' valid or should it be 'IV'?

In classical usage, IV is standard for 4 and IX for 9. However, IIII was historically common on clock faces and still appears there today. This converter accepts standard subtractive notation only.

Is my data sent to a server?

All conversions run locally in your browser using JavaScript. No data is sent to our servers.

Roman numeral to number converter

Convert any Roman numeral to its Arabic (decimal) equivalent instantly. Type any Roman numeral from I to MMMCMXCIX (1 to 3,999) and the converter shows the number in real time with validation. All conversion runs locally in your browser.

Enter a Roman numeral

How it works

To convert a number to Roman numerals, the tool repeatedly subtracts the largest possible Roman numeral value from the number and appends the corresponding symbol (including subtractive pairs like IV=4, IX=9, XL=40, XC=90, CD=400, CM=900). To convert Roman numerals to a number, each character is mapped to its value; a character is subtracted if the next character has a greater value. All processing runs in JavaScript in your browser.

Processing runs in your browser

All conversions happen locally in your browser tab. Our servers are not involved at any point.

Related operations

For working with fractional or mixed numbers, try the fraction calculator. To convert numbers between binary, hex, and decimal, use the number base converter. For unit conversions like inches to centimetres, see the unit converter.

Frequently asked questions

How do Roman numerals work?: Roman numerals use letters to represent values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Letters are generally written from largest to smallest, left to right. When a smaller value precedes a larger one, it is subtracted (e.g. IV=4, IX=9, XL=40, XC=90).
What is the largest number in Roman numerals?: Traditional Roman numerals can represent up to 3,999 (MMMCMXCIX). Numbers above 3,999 require a bar over letters to indicate multiplication by 1,000, which this converter does not support.
Is 'IIII' valid or should it be 'IV'?: In classical usage, IV is standard for 4 and IX for 9. However, IIII was historically common on clock faces and still appears there today. This converter accepts standard subtractive notation only.
Is my data sent to a server?: All conversions run locally in your browser using JavaScript. No data is sent to our servers.

Roman numeral to number converter

How it works

Processing runs in your browser

Related operations

Frequently asked questions

Related tools