How do Roman numerals work?

Roman numerals use letters to represent values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Numbers are formed by combining these letters following specific placement rules.

What is the maximum number I can convert?

The standard Roman numeral system represents numbers up to 3,999 (MMMCMXCIX). The tool supports the full standard range for both conversion directions.

Can I convert Roman numerals to decimal?

Yes. Enter a Roman numeral string like XLII and the tool converts it to the decimal equivalent (42). Invalid Roman numeral sequences are flagged with an error.

How does subtractive notation work?

When a smaller numeral appears before a larger one, it is subtracted. For example, IV means 5-1=4, and XC means 100-10=90. The tool uses correct subtractive notation.

Are lowercase Roman numerals accepted?

Yes. Enter Roman numerals in uppercase or lowercase. The tool normalizes the input and provides the correct conversion either way.

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Roman Numeral Converter

Convert between Roman and Arabic numerals

Number

Result

Output will appear here...

How to Use

Step 1

Enter Value

Type the value you want to convert in the input field

Step 2

Select Units

Choose the source and target units for your conversion

Step 3

See Conversion

The converted result appears instantly as you type

Step 4

Copy Result

Copy the converted value to use it in your work

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What Is Roman Numeral Converter?

Roman Numeral Converter is a free online tool that converts between Roman numerals and decimal numbers. Convert numbers like XLII to 42 and vice versa instantly.

Key Features

Convert decimal to Roman numerals and back. Support for numbers 1 to 3,999. Validates Roman numeral input for correctness. Instant conversion as you type. Clear error messages for invalid input.

Benefits

Quickly convert Roman numerals found in books, clocks, and monuments. Verify Roman numeral representations for academic work. Save time on manual conversion calculations.

Use Cases

Convert years in Roman numerals on buildings and monuments. Verify chapter numbering in books and outlines. Create Roman numeral sequences for ordered lists. Educational tool for learning Roman numerals.

Tips for Best Results

Remember the basic values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Subtractive pairs are IV, IX, XL, XC, CD, and CM. No numeral repeats more than three times in a row.