basic

Roman Numeral Converter

Bidirectional Roman numeral ↔ decimal conversion.

Convert between Arabic numbers (1–3,999) and Roman numerals — the calculator detects the direction automatically.

Daniel Oh By Daniel Oh
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
Was this helpful?

How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Standard subtractive notation: M = 1000, D = 500, C = 100, L = 50, X = 10, V = 5, I = 1, with subtractive pairs IV, IX, XL, XC, CD, CM.

In depth

Convert between Arabic numbers (1–3,999) and Roman numerals — the calculator detects the direction automatically.