H1_Roman Numeral Converter - Arabic to Roman & Back | MultiTool

How it works

Type an Arabic number and see its Roman form, or type Roman numerals and get the number back. Invalid or non-canonical inputs are flagged so you always get the standard form used today.

Reading Roman numerals without fear

Seven symbols — I, V, X, L, C, D, M — build every number, with one clever rule: when a smaller symbol precedes a larger one, it subtracts (IV = 4, IX = 9, XL = 40, CM = 900). Everything else adds. That single rule is the whole grammar.

• Where they still live: clock faces, book chapters and volume numbers, movie copyright dates and sequels (Rocky IV), the Super Bowl, monarchs and popes (Elizabeth II), and outlines.
• Clocks with IIII: many clock faces write four as IIII instead of IV — a tradition from visual balance (IV clutters the dial edge), not an error.
• There is no zero and no true standard beyond 3999 (MMMCMXCIX) — larger numbers need the overline notation you see in old texts, which is rarely used today.
• Reading tips: process the string right-to-left, subtracting when a symbol is smaller than its right neighbor — 30 seconds of practice makes it automatic.

The converter handles both directions with full validation — invalid forms (like IIII or VX) are rejected, not guessed.

Your privacy

Everything runs entirely in your browser. Nothing you type is ever sent to any server or stored.