How to Use Roman Numeral Converter

The Roman Numeral Converter converts between Roman numerals (I, V, X, L, C, D, M) and decimal numbers (1–3999) using standard subtractive notation (e.g. IV=4, IX=9).

What are Roman Numerals?

Roman numerals use letters to represent values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Subtractive notation uses IV for 4, IX for 9, XL for 40, XC for 90, CD for 400, CM for 900. This tool supports both directions.

Key Features

• Decimal to Roman (1–3999).
• Roman to decimal with validation.
• Case-insensitive Roman input.
• Client-side only.

How to Use

1. Open the Roman Numeral Converter tool.
2. Choose direction: Decimal → Roman or Roman → Decimal.
3. Enter the value and read the result.

Use Cases

• Outlines — Number sections with Roman numerals.
• Copyright — Format years in Roman form.
• Education — Learn or verify Roman numeral rules.

Frequently Asked Questions

What is this tool used for?

It converts between Roman numerals (I, V, X, L, C, D, M) and decimal numbers (1–3999), using standard subtractive notation.

What Roman format is supported?

Standard notation: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Input is case-insensitive.

What range of numbers?

Decimal to Roman supports 1–3999. Roman to decimal accepts any valid Roman numeral in that range.

Is conversion done on a server?

No. Conversion runs entirely in your browser.

When should I use it?

Use it for outlines, copyright years, or learning Roman numerals.

Why does Roman to decimal fail?

Ensure the string uses only I, V, X, L, C, D, M and follows standard order (e.g. no IIII for 4; use IV).

Conclusion

Use the Roman Numeral Converter for Roman ↔ decimal. See also Numbers to Words and Number Base Converter.