Roman Numeral ConverterFree online other calculator — instant results, no sign-up
Convert numbers to and from Roman numerals.
Sign in to save results and favorites.
About the Roman Numeral Converter
This calculator converts integers into standard Roman numerals and parses Roman numeral strings back into Arabic numbers. It is commonly used by students, historians, genealogists, and readers deciphering dates, book chapters, or copyright markers.
- Number or numeral
- An Arabic integer between 1 and 3999 (e.g., 2026) or a standard Roman numeral string (e.g., MMXXVI).
Formula and method
Standard additive-subtractive notation using values: M = 1000, CM = 900, D = 500, CD = 400, C = 100, XC = 90, L = 50, XL = 40, X = 10, IX = 9, V = 5, IV = 4, I = 1. Number = Σ(values where current ≥ next) − Σ(values where current < next).
- sInput text trimmed of leading and trailing whitespace
- roman(n)Conversion function mapping integer n (1 to 3999) to Roman numeral string
- unroman(s)Parsing function mapping Roman numeral string s back to an Arabic integer
The tool checks whether the trimmed input contains only digits using a regular expression. If digits are detected, it validates that the value is strictly between 0 and 4000 (1 to 3999 inclusive) and generates the Roman numeral equivalent; otherwise, it treats the input as a Roman numeral and parses it into an Arabic number.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Number or numeral2026
Results
- Roman numeralMMXXVI
How to use the Roman Numeral Converter
- 1Trim any whitespace from the input string.
- 2Test if the input consists solely of numeric digits.
- 3If numeric, verify the value is within 1 to 3999 and convert using standard Roman numeral mapping; return an error prompt if outside this range.
- 4If non-numeric, parse the Roman numeral string into its equivalent base-10 integer.
Reading your result
When an Arabic integer is supplied, the result shows the formatted Roman numeral under the label 'Roman numeral' (or 'Use 1–3999' if out of bounds). When letters are supplied, the result outputs the converted base-10 value under the label 'Number'.
Limitations
The Arabic-to-Roman conversion only supports whole integers from 1 to 3999, as standard Roman numerals have no zero, negative numbers, or fraction notations. It does not support vinculum (bar notation) for numbers 4,000 and above.
Common questions
Why is the input range limited to 1 through 3999 for number-to-numeral conversion?+
Standard Roman numerals use M for 1,000 and typically repeat up to three times (MMM = 3,000). Representing 4,000 and above traditionally requires extended bar notations (vinculum), which standard character sets do not support.
Can this tool convert the number zero?+
No. Classical Roman numerals did not include a symbol for zero, so the converter requires positive integers starting at 1.
Is the numeral input case-sensitive?+
The parser accepts standard Roman numeral letter characters regardless of case, converting combinations of I, V, X, L, C, D, and M into an integer.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
You might also like
Conversion Calculator
Convert length, weight, volume and area units.
Shoe Size Conversion
Convert shoe sizes between US, UK and EU.
Tire Size Calculator
Diameter and circumference from a tire code.
Temperature Converter
Convert Celsius, Fahrenheit and Kelvin.
Energy Converter
Convert standard energy units.
Power Converter
Convert standard power units.
Results are estimates for informational purposes and are not financial, medical or legal advice.