🏛️ Roman Numeral Converter
Roman numerals still appear on clock faces, book chapters, movie sequels and cornerstones. Enter a number from 1 to 3999 to get its Roman form, or flip the mode to decode a numeral back to digits.
Invalid numerals are rejected with an explanation, so MMXXVI works but IIII does not.
How to use this calculator
Type a value and choose the direction: Number to Roman or Roman to Number. The converter validates the input and returns the converted result.
- Type the Value, for example 2026 or MMXXVI.
- Choose the Direction of conversion.
- Read the result instantly.
- If the input is invalid you will get a clear error message.
Frequently asked questions
What does the Roman Numeral Converter do?
In Number to Roman mode it converts integers from 1 to 3999 into Roman numerals. In Roman to Number mode it decodes a Roman numeral back into digits, rejecting invalid forms.
What are the rules it follows?
Standard subtractive notation: I, X and C precede larger values to mean 4, 9, 40, 90, 400 and 900. Symbols repeat at most three times, so IIII is rejected in favor of IV.
Can you give a worked example?
2026 converts to MMXXVI, and MMXXVI converts back to 2026.
Why stop at 3999?
Traditional Roman numerals have no standard symbol above M = 1000, so 3999 (MMMCMXCIX) is the largest value expressible without extended notation like overlines.