Roman Numerals Converter: Number to Roman & Back

Roman Numerals Converter

Convert numbers ↔ Roman numerals, live both ways

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Standard Roman numerals use the symbols I=1, V=5, X=10, L=50, C=100, D=500, M=1000, combined additively and with subtractive pairs (IV=4, IX=9, XL=40, XC=90, CD=400, CM=900). Example: 1994 = MCMXCIV (M=1000, CM=900, XC=90, IV=4).

This system natively supports numbers 1 to 3,999. For numbers from 4,000 up to 3,999,999, this tool uses the traditional vinculum (overline) convention: a bar drawn over a numeral multiplies its value by 1,000. We represent the overline using the Unicode combining overline character, e.g. 4,000,000 is out of range, but 4,000 = ĪV̄ (an overlined "IV", meaning 4 × 1000). This is a display convention, not a universally standardized ASCII notation — treat overlined output as an approximation of the historical vinculum system.

Converting Roman → number validates standard subtractive notation rules (e.g. "IIII" or "VX" are rejected as invalid).

Number

Enter a whole number from 1 to 3,999,999.

Roman Numeral

Enter a valid Roman numeral using I, V, X, L, C, D, M.

🔧 Your Result

Roman Numeral

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Enter a number or Roman numeral above

Symbol Breakdown

Converting a number to Roman numerals by hand means juggling additive and subtractive rules, this converter handles both directions instantly, with validation to catch invalid Roman numeral input.

How to use this Roman numerals converter

Enter a whole number from 1 to 3,999,999 to see it in Roman numerals.
Or enter Roman numerals to see the equivalent number, either field updates the other live.

What this converter does

Standard Roman numerals use the symbols I=1, V=5, X=10, L=50, C=100, D=500, M=1000, combined additively and with subtractive pairs (IV=4, IX=9, XL=40, XC=90, CD=400, CM=900). For example, 1994 becomes MCMXCIV (M=1000, CM=900, XC=90, IV=4).

1994 = M(1000) + CM(900) + XC(90) + IV(4) = MCMXCIV

How numbers above 3,999 are handled

The standard Roman numeral system natively supports numbers 1 to 3,999. For numbers from 4,000 up to 3,999,999, this tool uses the traditional vinculum (overline) convention, a bar drawn over a numeral multiplies its value by 1,000. This is represented using the Unicode combining overline character, so 4,000 becomes an overlined “IV” (meaning 4 × 1000). This is a display convention reflecting historical practice, not a universally standardized ASCII notation, treat overlined output as an approximation of the historical vinculum system rather than a fixed modern standard.

Why Roman-to-number conversion includes validation

Converting Roman numerals back to a number validates standard subtractive notation rules, so invalid sequences like “IIII” (which should be “IV”) or “VX” are rejected rather than silently misinterpreted, ensuring the numeric result you get actually corresponds to a properly formed Roman numeral.

Frequently asked questions

What’s the largest number this converter supports?

Standard Roman numerals natively support 1 to 3,999. This tool extends that up to 3,999,999 using the traditional vinculum (overline) convention, where a bar over a numeral multiplies its value by 1,000.

Why does the converter reject “IIII” as an invalid Roman numeral?

Standard Roman numeral notation uses the subtractive form IV (4) rather than four consecutive I’s, this converter validates against standard subtractive notation rules and rejects non-standard sequences like IIII or VX.