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Roman Numeral Converter

Convert any number (1–3999) to Roman numerals, or type a Roman numeral to get its decimal value. Switch modes with the toggle. Step-by-step conversion shown for every result.

Convert:
255 = CCLV
Converting 255 to Roman numerals:

255 ≥ 100 → use C (subtract 100), remaining = 155
155 ≥ 100 → use C (subtract 100), remaining = 55
55 ≥ 50 → use L (subtract 50), remaining = 5
5 ≥ 5 → use V (subtract 5), remaining = 0

Result: CCLV
Decomposition: C=100 + C=100 + L=50 + V=5 = 255
Roman Numeral Reference:
SymbolValueNote
I1one
IV4four (subtractive)
V5five
IX9nine (subtractive)
X10ten
XL40forty (subtractive)
L50fifty
XC90ninety (subtractive)
C100hundred
CD400four hundred (subtractive)
D500five hundred
CM900nine hundred (subtractive)
M1000thousand

The Roman Numeral System

Roman numerals are a numeral system originating in ancient Rome that remained the dominant number notation in Europe well into the Late Middle Ages. Rather than a positional system like our modern decimal notation — where the value of a digit changes based on its position — Roman numerals use a combination of additive and subtractive notation with seven fixed symbols.

The system was in common use from approximately 500 BCE through the 14th century CE, when it was gradually replaced by Hindu-Arabic numerals (the 0–9 system we use today) following their introduction to Europe through Arabic mathematical manuscripts.

The Seven Symbols

The Roman numeral system uses seven letters from the Latin alphabet, each representing a specific value:

Symbol Value Origin
I 1 One finger (tally mark)
V 5 Likely the shape of an open hand (5 fingers)
X 10 Two V's crossed; or Greek letter chi
L 50 Uncertain; possibly a rotated V with a stem
C 100 Latin "centum" (hundred)
D 500 Half of the symbol for 1000 (a circle with vertical line)
M 1000 Latin "mille" (thousand)

Additive and Subtractive Notation

The primary rule is additive: combine symbols, largest to smallest, and add their values.

III = 1 + 1 + 1 = 3    VIII = 5 + 1 + 1 + 1 = 8    XVII = 10 + 5 + 1 + 1 = 17

Subtractive notation is used for six specific cases to avoid four-symbol repetition:

Rules for Valid Roman Numerals

How to Convert Numbers to Roman Numerals

The algorithm works by greedily subtracting the largest possible value at each step:

Example: Convert 2,024 to Roman numerals
Values to try (largest first): M=1000, CM=900, D=500, CD=400, C=100, XC=90, L=50, XL=40, X=10, IX=9, V=5, IV=4, I=1

2024 ≥ 1000 → write M, remaining = 1024
1024 ≥ 1000 → write M, remaining = 24
24 ≥ 10 → write X, remaining = 14
14 ≥ 10 → write X, remaining = 4
4 ≥ 4 → write IV, remaining = 0
Result: MMXXIV

Roman Numerals in Modern Use

Despite being replaced for arithmetic by Hindu-Arabic numerals (our Number System Converter handles binary, hex, and other modern bases), Roman numerals persist in several domains where tradition, formality, or aesthetics take precedence over practicality:

Context Examples
Annual events Super Bowl LVIII, Olympic Games
Monarchs and popes King Charles III, Pope Benedict XVI
Film copyright years © MMXXIV at the end of credits. Use our Age Calculator to find a film's age from its Roman numeral year
Clock faces I through XII (often IIII instead of IV)
Document outlines Chapter I, Section II, Part III
Building cornerstones Established MCMXLVII
Medical prescriptions Dosage notation in some traditions
Book front matter Preface pages numbered i, ii, iii, iv

Note the clock face curiosity: many clock manufacturers use IIII instead of the subtractive IV for the number 4. Theories for this include: aesthetic balance (three symbols on each quarter vs. two on one and four on the other), the historical fact that ancient Roman practice predated standardized subtractive notation, and the practical concern that IIII is easier to read upside-down on a clock face.

Frequently Asked Questions

How do you convert a number to Roman numerals?

To convert a number to Roman numerals, repeatedly subtract the largest Roman numeral value that fits and record the corresponding symbol. Example: 2024 → subtract 1000 (M) = 1024 → subtract 1000 (M) = 24 → subtract 10 (X) = 14 → subtract 10 (X) = 4 → subtract 4 (IV) = 0. Result: MMXXIV.

What is subtractive notation in Roman numerals?

Subtractive notation is a convention where a smaller symbol placed before a larger one means subtraction: IV = 5 − 1 = 4, IX = 10 − 1 = 9, XL = 50 − 10 = 40, XC = 100 − 10 = 90, CD = 500 − 100 = 400, CM = 1000 − 100 = 900. Only specific pairs are valid subtractive combinations — you cannot write IC for 99 (correct is XCIX) or VL for 45 (correct is XLV).

What is the largest number in Roman numerals?

Using the standard rules (no repetition of more than 3 of the same symbol, no bar notation), the largest number representable is 3,999 (MMMCMXCIX). Ancient Romans sometimes used a horizontal bar over a numeral to multiply by 1,000, extending the range significantly, but this is not standard in modern usage. Our calculator supports 1 to 3,999.

Why are Roman numerals still used today?

Roman numerals appear in several modern contexts: Super Bowl numbering (Super Bowl LVIII), copyright years in films and books, clock faces (often using IIII instead of IV for symmetry), outlines and lists, monarchs and popes (King Charles III, Pope Francis I), chapter numbering, and building cornerstone dates. They convey formality and tradition.

How do you read Roman numerals in movie copyright dates?

Movie copyright dates often appear as Roman numerals at the end of credits. Read them by identifying each symbol's value, then apply the subtractive rule: if a smaller value precedes a larger one, subtract; otherwise add. Example: MCMXCIX = M (1000) + CM (900) + XC (90) + IX (9) = 1999. MMXXVI = MM (2000) + XX (20) + VI (6) = 2026.

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