Roman Numeral Converter

Type a number to get its Roman numeral, or type a Roman numeral to get the number. It follows the standard subtractive notation (IV, IX, XL…) for values from 1 to 3999, and runs in your browser.

Enter a number or a Roman numeral.

How Roman numerals work

Roman numerals build numbers from seven letters: I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, M = 1000. Most values are written largest-to-smallest and added together, but to avoid four-in-a-row a smaller letter placed before a larger one is subtracted.

M=1000  D=500  C=100  L=50  X=10  V=5  I=1

So IV is 5−1 = 4 and IX is 10−1 = 9. The converter applies these rules greedily from the largest value down, which always yields the canonical form.

Worked example

Converting 2026:

2000 = MM.
20 = XX, and 6 = VI.
Result: 2026 = MMXXVI.

Rules and limits

Standard Roman numerals only have the subtractive pairs IV, IX, XL, XC, CD and CM, and no letter repeats more than three times in a row. There's no zero and no native way to write fractions, and the conventional range is 1 to 3999 (MMMCMXCIX) — larger numbers historically used an overline to multiply by 1000, which this tool doesn't use.

Tip: want a number written out in English words instead? Use the number to words converter.

Frequently asked questions

What's the largest number I can convert?

Standard Roman numerals go up to 3999, written MMMCMXCIX. Larger numbers historically used an overline (vinculum) to multiply by 1000, which isn't part of the common notation this tool uses.

Why is 4 written IV instead of IIII?

To avoid four of the same letter in a row, Roman numerals use subtractive notation: a smaller letter before a larger one is subtracted, so IV = 5 − 1 = 4. (Clock faces sometimes use IIII for style.)

Is there a Roman numeral for zero?

No. The system has no symbol for zero and no negative numbers, which is one reason place-value decimal numerals eventually replaced it for arithmetic.

Does it validate Roman numerals?

Yes. When converting back to a number, the tool checks the input is a well-formed standard numeral and reports an error for invalid sequences like IIII or VX.

MB
Mustafa Bilgic · Editor, Calcool
Uses standard subtractive Roman numeral notation for the conventional 1–3999 range. Input is validated for well-formed numerals. Everything runs in your browser — nothing you enter is uploaded, logged or stored.

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