Roman Numeral Converter

Written byOleh Soloninupdated 5 October 2026

Mode

Number (1-3999)

Result

Roman numeralMMXXVI
Arabic number2,026

Both directions, with the rules enforced

Convert 1 to 3999 into Roman numerals or read numerals back into numbers. Validates the input rather than accepting made-up forms.

Roman numerals survive on clock faces, film credits, book chapters and monuments. Reading them is easy until subtractive pairs appear — IX is nine, not eleven.

The system has real rules: only I, X, C and M repeat, and only certain subtractions are legal. This converter enforces them, so IIII comes back as invalid with IV offered instead.

How to use

Choose the direction: Arabic to Roman, or Roman to Arabic.
Enter the number or the Roman string.
Read the result; the calculator also validates the Roman form.

The subtraction rule and the ceiling

A smaller symbol before a larger one is subtracted: IV is 4, IX is 9, XL is 40. Only powers of ten may be subtracted, and only from the two symbols nearest above them, which is why 49 is XLIX rather than IL.

In the canonical form, where no symbol repeats more than three times in a row, the largest number is 3,999: M stands for a thousand and there is no ordinary symbol for five thousand. The converter works with that form. It has no zero either, and no negative numbers.

Worked out with this calculator.
Number	Roman	Breakdown
4	IV	5 − 1
49	XLIX	(50 − 10) + (10 − 1)
2026	MMXXVI	1000 + 1000 + 10 + 10 + 5 + 1
3999	MMMCMXCIX	the ceiling of the canonical form

What this calculator shows

Roman numerals for any number from 1 to 3999
The Arabic value of a numeral you enter
Validation that rejects non-canonical forms rather than guessing

What to keep in mind

Covers 1 to 3999, the standard range without overline notation.
There is no Roman numeral for zero — the concept did not exist in the system.

FAQs

Why is 4 written IV and not IIII?

Standard notation subtracts rather than repeating four times. Clock faces are the famous exception and often use IIII for visual balance.

What is the largest number I can write?

3999, or MMMCMXCIX. Beyond that Romans drew a bar over a numeral to multiply it by a thousand, which this converter does not support.

Which subtractions are actually allowed?

Only six: IV, IX, XL, XC, CD and CM. IC for 99 is not valid — that is XCIX.

How do I read MMXXVI?

2026. MM is 2000, XX is 20, V is 5 and I is 1.

How is 2026 written in Roman numerals?

MMXXVI — two thousands as MM, twenty as XX and six as VI. The subtraction rule never comes into it.

Why is 49 XLIX rather than IL?

Only powers of ten may be subtracted, and only from the two symbols immediately above them. So forty is XL, nine is IX, and the shortcut IL is not valid.

Worked example

A film copyright date

Input: 1994

Output: MCMXCIV

Note: Read in blocks: M is 1000, CM is 900, XC is 90, IV is 4. Three separate subtractive pairs in one date.

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