Roman Numeral Converter

Key features

• Converts numbers to Roman numerals and Roman numerals to numbers — a swap button flips direction without retyping.
• Standard subtractive notation (IV, IX, XL, XC, CD, CM), exactly as carved on monuments and clock faces.
• Strict parsing: malformed numerals like IIII or IC are rejected, not silently “corrected”.
• Case-insensitive input — “mmxxv” is uppercased automatically.
• Sample chips (4, 9, 14, 42, 99, 2025, 3999) for quick tests, plus a copy button on the result.

How it works

1. 1

   Choose the direction

   Tabs switch between Number → Roman and Roman → Number; the swap button toggles too.

2. 2

   Type your value

   A whole number from 1–3999, or a numeral built from M, D, C, L, X, V and I.

3. 3

   Read the result

   The conversion appears in large type with a copy button beside it.

4. 4

   Heed the validation

   Impossible numerals or out-of-range numbers get a specific error message rather than a wrong answer.

Tips for better results

• 💡Years make great test cases: 2025 → MMXXV and 1994 → MCMXCIV — the sample chips include the extremes.
• 💡If a numeral copied from the web is rejected, it probably uses non-standard notation (IIII instead of IV, or IC for 99); the round-trip check catches both.
• 💡The largest standard numeral is MMMCMXCIX (3,999) — the classical system has no symbol above M (1,000), so the tool stops there honestly.
• 💡Many clock faces use IIII instead of IV — that's a clockmaker's tradition, and this tool will correctly flag it as non-standard.

Frequently asked questions