How Do Roman Numerals Work? A Complete Guide

March 7, 2026

What Are Roman Numerals?

Roman numerals are a numeral system that originated in ancient Rome. They remained the standard way of writing numbers throughout Europe well into the Late Middle Ages. Even today, Roman numerals appear everywhere: on clock faces, in movie credits, for Super Bowl numbering, in the names of monarchs and popes, and as a popular choice for tattoos and inscriptions.

Unlike our modern decimal system (also called Arabic numerals or Hindu-Arabic numerals), which uses ten digits (0-9) and place value, Roman numerals use combinations of seven letters from the Latin alphabet to represent values. There is no zero in Roman numerals — the concept of zero was not introduced to Europe until centuries after the fall of Rome.

This guide will teach you everything you need to know about reading, writing, and converting Roman numerals, with plenty of examples and reference charts.

The Seven Symbols

The entire Roman numeral system is built on just seven symbols. Each symbol has a fixed value:

Symbol	Value	Origin
I	1	A single tally mark, representing one finger
V	5	Thought to represent an open hand (five fingers)
X	10	Two hands crossed, or two V shapes joined
L	50	Originally derived from a rotated or split form of the Greek letter chi
C	100	From the Latin word centum (hundred)
D	500	Half of the old symbol for 1000 (a circle with a line)
M	1000	From the Latin word mille (thousand)

These seven symbols can be combined to represent any number from 1 to 3,999 using standard notation. For numbers beyond 3,999, a system called vinculum (overline notation) is used, which we will cover later.

The Basic Rules

Roman numerals follow four fundamental rules for combining symbols into numbers:

Rule 1: Addition (Left to Right)

When a symbol of equal or greater value appears before another symbol, their values are added together. You read from left to right, adding as you go:

• VI = 5 + 1 = 6
• XII = 10 + 1 + 1 = 12
• LXV = 50 + 10 + 5 = 65
• MDCLXVI = 1000 + 500 + 100 + 50 + 10 + 5 + 1 = 1666

Rule 2: Subtraction (Smaller Before Larger)

When a smaller value appears directly before a larger value, the smaller value is subtracted from the larger one. This is called subtractive notation and is used to avoid writing four of the same symbol in a row:

• IV = 5 − 1 = 4 (instead of IIII)
• IX = 10 − 1 = 9 (instead of VIIII)
• XL = 50 − 10 = 40 (instead of XXXX)
• XC = 100 − 10 = 90
• CD = 500 − 100 = 400
• CM = 1000 − 100 = 900

Rule 3: Repetition Limit

A symbol can be repeated up to three times in a row to add its value. You never write a symbol four times consecutively in standard notation:

• III = 3 (correct)
• XXX = 30 (correct)
• CCC = 300 (correct)
• IIII = incorrect in standard notation (should be IV)

Note: The symbols V, L, and D are never repeated, because doubling them would equal the next higher symbol (VV = X, LL = C, DD = M).

Rule 4: Valid Subtractive Pairs

Not every symbol can be used in subtractive notation. Only I, X, and C can be placed before a larger symbol, and only before their next two higher symbols:

Subtractive Pair	Value	Used For
IV	4	I before V
IX	9	I before X
XL	40	X before L
XC	90	X before C
CD	400	C before D
CM	900	C before M

This means combinations like IL (49), IC (99), or IM (999) are not valid in standard Roman numeral notation, even though they might seem logical.

Step-by-Step: Converting Arabic to Roman Numerals

To convert a regular (Arabic) number to Roman numerals, break the number down by place value and convert each part:

Example 1: Convert 47 to Roman Numerals

1. 47 = 40 + 7
2. 40 = XL
3. 7 = VII
4. Result: XLVII

Example 2: Convert 399 to Roman Numerals

1. 399 = 300 + 90 + 9
2. 300 = CCC
3. 90 = XC
4. 9 = IX
5. Result: CCCXCIX

Example 3: Convert 1994 to Roman Numerals

1. 1994 = 1000 + 900 + 90 + 4
2. 1000 = M
3. 900 = CM
4. 90 = XC
5. 4 = IV
6. Result: MCMXCIV

Example 4: Convert 2026 to Roman Numerals

1. 2026 = 2000 + 20 + 6
2. 2000 = MM
3. 20 = XX
4. 6 = VI
5. Result: MMXXVI

Conversion Reference Table

Ones	Tens	Hundreds	Thousands
1 = I	10 = X	100 = C	1000 = M
2 = II	20 = XX	200 = CC	2000 = MM
3 = III	30 = XXX	300 = CCC	3000 = MMM
4 = IV	40 = XL	400 = CD
5 = V	50 = L	500 = D
6 = VI	60 = LX	600 = DC
7 = VII	70 = LXX	700 = DCC
8 = VIII	80 = LXXX	800 = DCCC
9 = IX	90 = XC	900 = CM

Converting Roman Numerals to Arabic Numbers

To convert Roman numerals back to regular numbers, read from left to right and apply the addition and subtraction rules:

Example: What number is MCMXLIV?

1. Start from the left: M = 1000
2. CM = 900 (C is less than M, so subtract: 1000 − 100)
3. XL = 40 (X is less than L, so subtract: 50 − 10)
4. IV = 4 (I is less than V, so subtract: 5 − 1)
5. Total: 1000 + 900 + 40 + 4 = 1944

Example: What number is CDLXXVIII?

1. CD = 400
2. L = 50
3. XX = 20
4. VIII = 8
5. Total: 400 + 50 + 20 + 8 = 478

Large Numbers: Vinculum Notation

Standard Roman numerals can only represent numbers up to 3,999 (MMMCMXCIX). For larger numbers, the Romans developed the vinculum system: a bar (overline) placed above a numeral multiplies its value by 1,000.

• V = 5,000
• X = 10,000
• L = 50,000
• C = 100,000
• D = 500,000
• M = 1,000,000

For example, 50,000 is written as L, and 1,000,000 is written as M.

A double overline multiplies by 1,000,000. This site supports numbers up to 999,999,999 using this extended notation.

Common Mistakes to Avoid

Here are the most frequent errors people make with Roman numerals:

• Writing IIII for 4 — The correct standard form is IV. However, IIII does appear on some clock faces, a tradition that dates back centuries. This is called the “watchmaker's four” and is not considered standard notation.
• Using IM for 999 — This seems logical (1000 − 1), but it violates Rule 4. The correct form is CMXCIX (900 + 90 + 9).
• Using IC for 99 — Same issue. The correct form is XCIX (90 + 9).
• Repeating V, L, or D — These symbols are never repeated. Write X instead of VV, C instead of LL, M instead of DD.
• Using more than three of the same symbol — XXXX is wrong; write XL instead.
• Wrong subtraction order — The subtractive symbol always comes first (before the larger value), never after. MX is 1010, not 990.

Roman Numerals in Daily Life

Roman numerals remain surprisingly common in everyday life:

• Clocks and watches — Many clock faces use Roman numerals, with IV sometimes shown as IIII.
• Super Bowl — The NFL uses Roman numerals to number each Super Bowl (e.g., Super Bowl LVIII).
• Monarchs and popes — Henry VIII, Louis XIV, Elizabeth II, Pope Francis (the first of his name, so no numeral).
• Movie and TV sequels — Rocky II, Star Wars Episode IV, The Godfather Part III.
• Copyright dates — Many films and TV shows display the production year in Roman numerals in their credits.
• Outlines and lists — Academic and legal documents often use Roman numerals for section numbering.
• Tattoos — Roman numerals are one of the most popular tattoo choices, especially for birth years, anniversaries, and meaningful dates like MCMXC or MM.
• Architecture — Building cornerstones and monuments often feature the year of construction in Roman numerals.

Quick Reference Charts

Roman Numerals 1 to 20

Number	Roman	Number	Roman
1	I	11	XI
2	II	12	XII
3	III	13	XIII
4	IV	14	XIV
5	V	15	XV
6	VI	16	XVI
7	VII	17	XVII
8	VIII	18	XVIII
9	IX	19	XIX
10	X	20	XX

Tens: 10 to 100

Number	Roman
10	X
20	XX
30	XXX
40	XL
50	L
60	LX
70	LXX
80	LXXX
90	XC
100	C

Hundreds: 100 to 1000

Number	Roman
100	C
200	CC
300	CCC
400	CD
500	D
600	DC
700	DCC
800	DCCC
900	CM
1000	M

Try the Converter

Use our converter to instantly translate any number to Roman numerals (or vice versa). Just type a number or Roman numeral below: