Roman Numeral Converter — Decimal ↔ Roman Numbers Instantly

What Is a Roman Numeral Converter?

A Roman Numeral Converter translates numbers between the standard decimal system (Arabic numerals) and the classical Roman numeral system — entirely in your browser. No data is sent to any server.

Roman Numeral Symbols

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

Subtractive Notation

To avoid four consecutive identical symbols, Roman numerals use subtractive pairs:

Notation	Value
IV	4
IX	9
XL	40
XC	90
CD	400
CM	900

A smaller symbol placed before a larger one means subtraction. For example, IX = 10 − 1 = 9 and CM = 1000 − 100 = 900.

How to Use

Type a decimal number (1–3999) and the Roman numeral appears instantly.
Type a Roman numeral (e.g. MCMXCIV) and the decimal value is shown.
Use Batch Convert to process multiple values at once — one per line, mix of decimal and Roman.
Click Copy to copy either result to your clipboard.

Rules for Valid Roman Numerals

Only the symbols I, V, X, L, C, D, M are allowed.
I, X, C, M may appear up to three times consecutively (e.g. III, XXX, CCC, MMM).
V, L, D may never repeat.
Only the six standard subtractive pairs are valid (IV, IX, XL, XC, CD, CM).

Invalid examples: IIII, MMMM, VV, LL, DD, IIX, VX.

Decimal to Roman: Step-by-Step

Converting 1994 to MCMXCIV:

Remaining	Symbol	Result so far
1994	M	M
994	CM	MCM
94	XC	MCMXC
4	IV	MCMXCIV

The algorithm greedily subtracts the largest possible value at each step.

Roman to Decimal: Step-by-Step

Reading XIV left to right:

X = 10
I = 1, but the next symbol V = 5 is larger → subtract: −1
V = 5

Total: 10 − 1 + 5 = 14

Whenever a symbol is followed by a larger one, it is subtracted rather than added.

The Supported Range: 1–3999

Standard Roman numerals cover 1 (I) to 3999 (MMMCMXCIX). Three Ms (MMM) is the highest repeating group. Numbers from 4000 upward require the vinculum (bar notation) or other historical extensions.

Common Uses

Numbering chapters, sections, and appendices in books and legal documents
Clock faces (I through XII)
Copyright years in film credits (e.g. MMXXIV = 2024)
Naming sequels, Super Bowls, and Olympic games
Numbering monarchs and popes (Henry VIII, Pope John Paul II)

Privacy

All conversions are computed locally in your browser. Nothing you type is ever sent to a server, stored, or tracked.

FAQ

What is the range of standard Roman numerals?

Standard Roman numerals cover 1 to 3999 (MMMCMXCIX). The symbol M represents 1000, and three Ms (MMM = 3000) is the largest repeating group allowed. Numbers 4000 and above require vinculum (bar) notation or other extensions not covered by the classical system.

Why is 4 written as IV and not IIII?

Subtractive notation is used to avoid four consecutive identical symbols. IV means "one before five" (5 − 1 = 4). The six subtractive pairs are: IV (4), IX (9), XL (40), XC (90), CD (400), and CM (900). IIII was historically used on clock faces and in some old manuscripts, but is not considered standard today.

Which Roman numeral symbols cannot be repeated?

V (5), L (50), and D (500) may never be repeated. I, X, C, and M may appear up to three times consecutively. Using four identical symbols like IIII or MMMM makes a numeral invalid in the standard system.

How do I convert a number larger than 3999?

Numbers above 3999 are not supported by standard Roman numerals. Historically, a bar placed over a numeral (vinculum) multiplied its value by 1000 — so V̄ = 5,000 and X̄ = 10,000. This tool covers the standard range 1–3999 only.

Is my data sent to a server?

No. All conversions happen entirely in your browser using JavaScript. Nothing you enter is sent to any server, stored, or logged.