Convert numbers and Roman numerals both ways. This free Roman numeral converter handles 1 to 3999, validates the numeral so only correct forms are accepted, and shows the expanded value of each symbol.
Standard Roman numerals run from 1 (I) to 3999 (MMMCMXCIX). Enter a number to get its Roman form, or a Roman numeral to read it as a number.
The seven symbols are I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. A smaller symbol before a larger one means subtraction (IV = 4, IX = 9, XL = 40, CM = 900).
What This Roman Numeral Converter Does
Convert a number into its Roman numeral form, or convert a Roman numeral back into a number, both within the standard range of 1 to 3999. Entered Roman numerals are validated, so malformed forms are flagged rather than silently misread.
The Seven Roman Numeral Symbols
I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Every standard Roman numeral is built from combinations of these seven symbols.
Additive and Subtractive Notation
Most of the time, symbols are added together in descending order (VI = 5 + 1 = 6). But when a smaller symbol appears immediately before a larger one, it’s subtracted instead (IV = 5 – 1 = 4, IX = 10 – 1 = 9, XL = 50 – 10 = 40, CM = 1000 – 100 = 900).
A Worked Example
The year 2024 converts to MMXXIV: MM = 2000, XX = 20, IV = 4. Combined, that’s 2000 + 20 + 4 = 2024.
Why Some Numeral Forms Are Invalid
Standard Roman numeral rules don’t allow certain repetitions or combinations, like writing 4 as “IIII” instead of “IV.” This converter checks that an entered numeral matches its own canonical re-encoded form, catching invalid or non-standard numerals rather than accepting anything that merely adds up to the right total.
Why the Range Stops at 3999
Standard Roman numeral notation has no symbol for numbers 4000 and above without extending the system (such as adding a bar over a numeral to multiply it by 1000). This converter covers the standard 1-3999 range used in dates, clock faces, and formal numbering.
How to Use the Roman Numeral Converter
- Choose a direction: Number to Roman, or Roman to Number.
- Enter your value in the field provided.
- Review the result along with the expanded symbol breakdown.
Working with other number systems too? See our Scientific Notation Converter.