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Roman Numeral Converter

Convert a number to Roman numerals or read a Roman numeral back to a number, both directions live.

A whole number from 1 to 3999.

Upper or lower case both work.

Reference

I1
V5
X10
L50
C100
D500
M1000

Subtractive pairs IV = 4, IX = 9, XL = 40, XC = 90, CD = 400, CM = 900

How to convert Roman numerals online

  1. Type a number

    Enter any whole number from 1 to 3999 in the number field to see its Roman numeral straight away.

  2. Or type a Roman numeral

    Type a numeral like XIV in the Roman field instead, in upper or lower case, and read the number it stands for.

  3. Copy the result

    Use the copy button beside either field to put the number or the numeral on your clipboard.

Why use this tool

Both directions, live

Edit either field and the other updates as you type. Numbers become numerals and numerals become numbers without a convert button.

Strict validation that names the rule

Malformed input like IIII, VX, or IL is rejected with a short note about the rule it breaks, so you learn why it is wrong rather than getting a silent wrong answer.

Honest 1 to 3999 range

Standard Roman numerals run from I to MMMCMXCIX. Numbers outside that range get a plain message instead of a made-up numeral.

Lowercase welcome

Type mmxxiv or xiv and it is read the same as the uppercase form, then shown back in standard uppercase.

Reference table on the page

The seven base letters and the six subtractive pairs sit under the fields, so you can check a numeral by hand without leaving.

Nothing leaves your browser

The conversion runs on your device. No numbers or numerals are uploaded, logged, or stored.

About this tool

A Roman numeral converter turns an ordinary number into the letter form the Romans used, and reads that form back into a number. It is the tool you want when a cornerstone reads MCMXLVIII, when a film ends on a copyright line in numerals, or when a clock face, a Super Bowl, or a monarch is numbered the old way. Type 2024 and you get MMXXIV; type XIV and you get 14. Both fields stay in sync, so you can work from whichever end you have.

Reading them by hand comes down to two ideas. Seven letters carry fixed values: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. You add letters from largest to smallest, except for six subtractive pairs where a smaller letter sits before a larger one to mean the difference. That is why 4 is IV, not IIII, and 9 is IX. This is also the honest source of the clock-face debate: strict notation writes 4 as IV, yet many clocks show IIII for visual balance, so both turn up in the wild.

Standard notation stops at 3999, written MMMCMXCIX, because there is no single letter above M and the rules cap M at three in a row. Larger values historically used a bar over a letter to multiply it by a thousand, which this converter does not use, so anything above 3999 gets a plain out of range note. The validation is picky: it rejects impossible numerals and tells you which rule broke. If you also work in other number systems, the number base converter handles binary and hex, and for dates written in numerals the date difference calculator and age calculator do the arithmetic once you have the year.

Frequently asked questions

How do Roman numerals work?
Seven letters have fixed values: I is 1, V is 5, X is 10, L is 50, C is 100, D is 500, and M is 1000. You add them from largest to smallest, with six subtractive pairs (IV, IX, XL, XC, CD, CM) where a smaller letter before a larger one means the difference.
Why is 4 shown as IV and not IIII?
Strict notation writes 4 as IV, using the subtractive rule, and that is what this converter produces. Many clock faces show IIII instead for visual balance, so you will see it in the wild, but IIII is not standard and is rejected here.
What numbers can it convert?
Whole numbers from 1 to 3999, which is the full range of standard Roman numerals. The largest is MMMCMXCIX. Anything outside that range gets a plain message rather than an invented numeral, since standard notation has no single letter above M.
Does it accept lowercase numerals?
Yes. Type xiv or mmxxiv and it is read the same as the uppercase form. The result is shown back in standard uppercase.
What happens if I type an invalid numeral?
Input like IIII, VX, or IL is rejected with a short note naming the rule it breaks, such as I can only precede V and X. You get the reason instead of a wrong number.
Is anything uploaded to a server?
No. The conversion runs entirely in your browser. Nothing you type is sent anywhere or stored.

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