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Roman Numeral Converter

Convert between Roman numerals and Arabic numbers with validation.

How to Use Roman Numeral Converter

  1. 1

    Enter a number

    Type a decimal number or Roman numeral to convert.

  2. 2

    See the conversion

    View the result instantly as you type in either direction.

  3. 3

    Copy the result

    Click copy to grab the converted Roman numeral or number.

Tested tool guide Math and conversion tools Checked July 30, 2026

What Roman Numeral Converter does, with a checked example

The converter recognizes decimal integers and the Roman symbols I, V, X, L, C, D, and M. Decimal input is expressed with standard subtractive pairs such as IV, IX, XL, XC, CD, and CM. Roman input is totaled from left to right and compared with the canonical form.

Worked example

A concrete input and expected output from the current implementation.

Input

2026

Expected output

MMXXVI

Two M symbols contribute 2,000, two X symbols contribute 20, V contributes 5, and I contributes 1.

How the result is produced

1

Largest values are consumed first

Decimal conversion walks a table from M through I, including subtractive pairs. It repeatedly appends the largest symbol that does not exceed the remaining number.

2

Noncanonical input is identified

Roman letters are summed with smaller values before larger ones subtracted. Re-converting the total reveals the conventional canonical spelling when the entered sequence differs.

Good uses

  • Check a date or chapter number written with Roman symbols.
  • Generate a canonical numeral for an integer.
  • Learn the common subtractive pairs with the reference table.

Limits and checks

  • The page supports the conventional range 1 through 3999.
  • Historical Roman usage was not completely standardized.
  • A sequence can be numerically interpretable but noncanonical.

Common questions

Why is 4 written IV instead of IIII?

Modern canonical notation commonly uses subtractive form: I before V subtracts one from five. Historical inscriptions sometimes used IIII.

How is zero written in Roman numerals?

Classical Roman numeral notation has no standard zero symbol, so this converter starts at 1.

References and verification

The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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