Roman Numeral Converter

What is a Roman numeral converter?

A Roman numeral converter translates between our everyday Arabic numbers (1, 2, 3…) and the Roman numerals (I, II, III…) still used for clock faces, book chapters, film sequels, monarch names and copyright years. This tool goes both ways: enter a number from 1 to 3999 to see its numeral, or enter a numeral to read the number back. It also shows how each numeral is assembled and flags invalid input instead of guessing.

How Roman numerals work

Roman numerals are built from seven letters, each with a fixed value:

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

You form a number by writing these largest-first and adding them up — so MCC is 1000 + 100 + 100 = 1200. To avoid four identical letters in a row, the system uses subtractive notation: a smaller letter before a larger one is subtracted. That gives the six special pairs IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). There is no symbol for zero, which is why the range starts at 1.

How the converter works

The number → Roman direction greedily subtracts the biggest value it can at each step, appending the matching symbol, until nothing is left. That's why the tool can show you the breakdown: 1994 comes out as M + CM + XC + IV.

The Roman → number direction reverses the process and then double-checks itself. After it works out a value, it converts that value back to a numeral; if the result doesn't match your exact input, your numeral wasn't standard, so you get a clear error rather than a wrong number. This round-trip check is what catches mistakes like IIII (should be IV) or IC (should be XCIX).

How to use it

1. In Number → Roman, type a whole number from 1 to 3999. The numeral appears immediately, along with the plus-by-plus breakdown.
2. In Roman → Number, type a numeral — lowercase is fine, it's read as uppercase. The number appears, or an error explains what's wrong.
3. Use each section's Copy button to grab that result, and Clear to reset both fields.

A worked example

Take the year 1994. Working largest-first:

• 1994 − 1000 = 994 → M
• 994 − 900 = 94 → CM
• 94 − 90 = 4 → XC
• 4 − 4 = 0 → IV

Put the pieces together and you get MCMXCIV. Paste that back into the second box and it round-trips cleanly to 1994. For switching between binary, hex and other bases, the Number Base Converter is the companion tool; for physical quantities, try the Unit Converter; and for share-of-a-number maths, the Percentage Calculator is a click away.

A note on edge cases

Classic Roman numerals stop being tidy above 3999 — larger values traditionally add an overbar to multiply by a thousand, which isn't part of plain-text notation, so this tool caps at 3999. There's also no representation for zero or for fractions in the standard system. Within its range, though, the output is the strict, widely accepted form you'll see on monuments and in credits.

Private by design

Both conversions run in your browser with plain JavaScript. Nothing you enter is uploaded, stored or shared — your numbers and numerals stay on your device. Explore more converters and number tools on the all tools page.