How to Convert Roman Numerals and Arabic Numbers

What the Roman numerals converter does

Roman numerals and Arabic numbers express the same values in different formats. Use this converter when you need to translate a whole number into Roman notation or check a Roman numeral by converting it back to an integer. The tool supports both directions, so you can choose the direction that matches the value you have.

For numeric input, conversion to a Roman numeral accepts integers from 1 through 3999. Roman numeral input is checked against valid characters and the canonical form recognized by the converter, which helps distinguish a standard Roman numeral from a malformed or noncanonical string.

How to convert a number or Roman numeral

1. Enter a value in the input field. You may enter an integer for Roman numeral output or a Roman numeral for numeric output. Leaving the field empty does not supply a usable conversion value, so enter the value you want to check.

2. Select the conversion direction. Choose the option for converting an integer to a Roman numeral when your input is numeric. Choose the option for converting a Roman numeral to an integer when your input uses Roman notation. If no direction is selected, the converter defaults to integer-to-Roman conversion.

3. Submit the conversion using the available control. For integer-to-Roman conversion, use a whole-number value from 1 to 3999. Values outside that range, or text that cannot be parsed as an integer, fail in this direction.

4. For Roman numeral input, surrounding spaces are removed and lowercase letters are treated as uppercase. The remaining value must use valid Roman numeral characters and match the canonical form accepted by the converter. Empty, invalid, or noncanonical input fails.

5. Review the returned values and selected direction. A successful result includes the numeric form, the Roman numeral form, and the conversion direction. A mode other than the two supported directions does not produce a successful conversion.

How to interpret the result

Read the result according to the direction you selected. With integer-to-Roman conversion, the numeric form reflects the parsed integer and the Roman form gives its Roman-numeral representation. With Roman-to-integer conversion, the Roman form is shown alongside its numeric value and the selected reverse direction.

If the converter reports a failure, first check the input format and the selected direction. Numeric conversion needs a parseable integer within the stated range. Roman input needs a canonical Roman numeral after surrounding whitespace and letter case are normalized. The numeric range stated for integer-to-Roman conversion should not be applied as a separate upper-bound rule to Roman-numeral parsing.

Worked example

You need to check the Roman-numeral representation of the year 2024 before using it in a heading.

Enter 2024, select integer-to-Roman conversion, and submit the value.

A successful result reports the numeric form, the Roman numeral form, and the selected integer-to-Roman conversion direction. The Roman numeral representation of 2024 is MMXXIV.

Limitations

• Integer-to-Roman conversion is limited to integers from 1 through 3999. Roman input must be canonical after normalization, and unsupported conversion directions fail.

Common errors

• A frequent input mistake is using a value outside 1 through 3999 for integer-to-Roman conversion or entering a noncanonical Roman form. Correct it by checking the direction, using a parseable integer in range, or entering the standard Roman form; surrounding spaces and lowercase letters are normalized for Roman input.

FAQ

How do I convert an Arabic number to a Roman numeral?

Select integer-to-Roman conversion and enter a parseable integer from 1 through 3999. Values outside that range fail for this direction.

How do I convert a Roman numeral to an Arabic number?

Select Roman-to-integer conversion and enter a canonical Roman numeral. Surrounding spaces are removed and lowercase letters are treated as uppercase, but empty, invalid, or noncanonical input fails.

What happens if I do not choose a conversion direction?

The default direction is integer-to-Roman conversion. Choose the other supported direction before submitting when your input is a Roman numeral.