Roman Numeral Converter: Convert Between Roman Numerals and Decimal Numbers

Roman numerals appear on clock faces, movie credits, book chapters, Super Bowl titles, and building cornerstones. Converting them by hand is straightforward for small values like VII (7) but gets tedious for longer ones like MCMXCIV (1994). Our converter handles both directions instantly, supporting every value from 1 to 3999.

How Roman Numerals Work

Roman numerals use seven symbols, each with a fixed value:

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

The Addition Rule

When a symbol of equal or greater value follows another, you add the values:

VIII = 5 + 1 + 1 + 1 = 8
CLX  = 100 + 50 + 10 = 160

The Subtraction Rule

When a smaller symbol precedes a larger one, you subtract the smaller from the larger. Only certain subtractive pairs are valid:

IV = 5 - 1  = 4      (not IIII)
IX = 10 - 1 = 9      (not VIIII)
XL = 50 - 10 = 40    (not XXXX)
XC = 100 - 10 = 90   (not LXXXX)
CD = 500 - 100 = 400 (not CCCC)
CM = 1000 - 100 = 900(not DCCCC)

Worked Example

Breaking down a complex numeral step by step:

MCMXCIV = ?

M   = 1000
CM  = 900  (1000 - 100)
XC  = 90   (100 - 10)
IV  = 4    (5 - 1)

Total: 1000 + 900 + 90 + 4 = 1994

Why 1 to 3999?

Standard Roman numeral notation has no symbol for zero and no way to represent 4000 or above without extensions (like the vinculum, a bar placed over a numeral to multiply its value by 1000). The valid range using the standard seven symbols is 1 through 3999 (MMMCMXCIX).

Our converter enforces this range and validates that the Roman numeral you enter follows the correct formation rules.

Where Roman Numerals Still Appear

Despite being over two thousand years old, Roman numerals remain surprisingly common:

• Clock and watch faces: Nearly all analog clocks use Roman numerals for the hours
• Film and television: Copyright years in movie credits (MMXXVI = 2026)
• Outlines and lists: Academic papers, legal documents, and formal outlines use Roman numerals for hierarchical numbering
• Sporting events: The Super Bowl, Olympic Games numbering
• Monarchs and popes: Henry VIII, Pope John XXIII, Queen Elizabeth II
• Architecture: Cornerstones and building inscriptions often show the year in Roman numerals
• Book chapters and volumes: Volume III, Chapter IX

How to Use Our Roman Numeral Converter

1. Choose your direction: Enter a Roman numeral or a decimal number
2. Type your value into the input field
3. See the result appear instantly as you type
4. Review the breakdown showing how each part was converted
5. Copy the result with one click

Features

• Bidirectional conversion: Roman to decimal and decimal to Roman
• Input validation: Flags invalid Roman numeral sequences (like IC or VV)
• Step-by-step breakdown: See exactly how each portion of the numeral maps to its value
• Real-time updates: Results appear as you type, no submit button needed

Tips

• The converter accepts both uppercase and lowercase input (iv, IV, and Iv all work)
• If you enter an invalid Roman numeral, the tool will tell you what is wrong with it
• For decimal to Roman conversion, enter any integer from 1 to 3999
• All computation happens in your browser — your input is never sent to a server

Quick Reference Table

Decimal	Roman	Decimal	Roman
1	I	50	L
4	IV	90	XC
5	V	100	C
9	IX	400	CD
10	X	500	D
40	XL	900	CM
49	XLIX	1000	M
2026	MMXXVI	3999	MMMCMXCIX

Frequently Asked Questions

Is there a Roman numeral for zero? No. The Roman numeral system was developed before the concept of zero was adopted in Western mathematics. There is no symbol or combination that represents zero.

Why do some clocks show IIII instead of IV for 4? This is called the “watchmaker’s convention.” Several theories exist: visual balance with VIII on the opposite side, easier reading at a glance, or historical tradition predating the subtractive rule. Both IIII and IV are considered acceptable on clock faces.

Can Roman numerals represent fractions or decimals? The ancient Romans did have a system for fractions based on twelfths (the uncia), but it is not part of the standard notation used today. Modern Roman numeral usage is limited to positive integers.

What is the largest number you can write in standard Roman numerals? 3999, written as MMMCMXCIX. To represent larger numbers, the vinculum system places a bar over numerals to multiply by 1000, but this is an extension beyond the standard seven symbols.

Is MCMXCIX the same as MIM? No. MIM is not valid in standard Roman numeral notation. The subtraction rule only applies to specific pairs (I before V/X, X before L/C, C before D/M). Jumping multiple levels, like I before M, is not permitted.

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Try our free Roman Numeral Converter to convert between Roman numerals and decimal numbers instantly.