Roman Numeral Converter

Convert between Arabic numbers and Roman numerals in both directions. The validator only accepts standard modern notation and explains what is wrong with an invalid numeral.

How to use the Roman Numeral Converter

1. Choose Number → Roman or Roman → Number.
2. Type a whole number from 1 to 3999, or a Roman numeral.
3. Read the converted value instantly.
4. Check the breakdown to see how the numeral is built.

Features

• Both directions in one tool
• Strict standard-form validation
• Clear explanations for invalid numerals
• Step-by-step breakdown (M + CM + XC + IV)

Benefits

• Read dates on buildings, clocks and film credits
• Check numbering for outlines and book chapters
• Learn the rules of Roman numerals by example

Frequently asked questions

Why is the limit 3999?

Standard Roman numerals have no symbol above M (1000) and a symbol may repeat at most three times, so MMMCMXCIX (3999) is the largest value.

Why is IIII rejected?

In standard notation 4 is written IV. IIII appears on some clock faces, but it is not the accepted form for numbers.

Which subtractive pairs are allowed?

Only IV, IX, XL, XC, CD and CM. Forms such as IC, VX or XM are not valid.

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