Roman Numeral Converter

Convert a number to Roman numerals or read a Roman numeral back as a number, with full validation of the standard 1–3999 range. Calculates in your browser.

Roman numeral

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How Roman numerals work

Seven letters carry values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. They are added left to right, except when a smaller letter sits before a larger one (like IV=4 or CM=900), where it is subtracted.

Standard Roman numerals run from 1 to 3999 and have one correct spelling each, so IIII is rejected in favour of IV.

What this does

A Roman numeral converter turns a number into Roman numerals or reads a numeral back as a number, validating the standard 1–3999 range that the classic system can represent.

How to use it

  1. Enter a number to get its Roman numeral.
  2. Or enter a numeral to read it as a number.
  3. Copy the validated result.

How it works

Letters add left to right (I, V, X, L, C, D, M), except a smaller letter before a larger one, which is subtracted. Each number has exactly one canonical spelling, so non-standard forms like IIII are rejected when reading.

Example

4 is IV, 9 is IX, 40 is XL, and 1994 is MCMXCIV. The supported range is 1 to 3999.

Sources & methodology

Last updated .

Frequently asked questions

What range is supported?

Standard Roman numerals cover 1 to 3999. The classic system has no symbol for zero or for numbers of 4000 and above without overlines.

How does subtractive notation work?

A smaller letter before a larger one is subtracted: IV is 4, IX is 9, XL is 40, and CM is 900. Otherwise letters are added left to right.

Why is IIII rejected?

Each number has exactly one standard spelling. Four is written IV, not IIII, so the tool only accepts the canonical form when reading numerals.

Is my data stored?

No. Everything is calculated locally in your browser.