123
VII

🎯 Roman Numeral Quiz

What is this in Arabic numbers?

Roman Numeral Converter

Convert integers to Roman numerals and back instantly. See the logic behind every calculation and master the ancient system used on clocks, architecture, and movie credits.

Why use this tool?

Don't just get the answer—understand it. Whether you're deciphering "MCMXCVIII" on a movie screen or designing a classic watch face, this tool breaks down the math behind the symbols so you can learn as you go.

Key Features

  • Convert both ways: Enter a standard number (1–3,999) to get its Roman equivalent, or type Roman letters to find the numeric value.
  • Analyze the logic: See exactly how each number is constructed. The tool explains that IX is 10 - 1, making the "why" clear.
  • Validate your entries: Stay accurate with strict adherence to classical rules. The tool flags invalid sequences like "IIII" as errors.
  • Test your skills: Use the built-in quiz mode to practice reading and writing Roman numerals on the fly.

FAQ

Can it handle numbers larger than 3,999? Standard Roman numerals without special diacritics (like overlines/vinculum) stop at 3,999 (MMMCMXCIX). To ensure universal compatibility, this tool focuses on the standard 1–3,999 range.

Why do some clocks use 'IIII' instead of 'IV'? This is known as the "Clockmaker's Four." It is often used for visual symmetry with the 'VIII' on the opposite side of the dial. While common in horology, 'IV' is the standard subtractive form used in mathematics and this tool.

Does capitalization matter? No. You can type in lowercase or uppercase. The tool automatically processes your input and displays the result in traditional uppercase.

The Subtractive Rule

The Roman numeral system is primarily additive (VI = 5 + 1), but the "Subtractive Rule" was standardized to prevent four identical symbols from appearing in a row.

  • I can be placed before V and X to make 4 and 9.
  • X can be placed before L and C to make 40 and 90.
  • C can be placed before D and M to make 400 and 900.

While these rules varied in the medieval period, modern usage—and this tool—follows the strict "Classical" format.