Roman Numeral Converter
PrintStandard Roman Numeral Values
| Roman Numeral | Arabic Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1,000 |
Roman numerals are an ancient numeral system that originated in ancient Rome and remained the standard method of writing numbers across Europe throughout the Middle Ages until Arabic numerals (0–9) replaced them during the 14th century. Today, Roman numerals are still used for book chapters, clock faces, monarch titles (e.g., King Charles III), building cornerstone dates, and major sporting events like the Super Bowl and Olympic Games.
Our free online Roman Numeral Converter provides two conversion modes:
- Standard Number Converter: Converts integers up to 3,999,999 to and from Roman numerals (using standard symbols and Vinculum overlines).
- Roman Numeral Date Converter: Converts full dates (YYYY/MM/DD, MM/DD/YYYY) or mixed calendar formats between Arabic numbers and Roman numerals.
The 7 Basic Roman Numeral Symbols
The modern Roman numeral system relies on seven basic uppercase Latin letters to denote powers of ten and their midpoints:
| Roman Numeral | Symbol Name | Arabic Equivalent Value | Mathematical Base |
|---|---|---|---|
| I | Unus | 1 | 100 Unit |
| V | Quinque | 5 | 5 × 100 Half-step |
| X | Decem | 10 | 101 Base |
| L | Fifty | 50 | 5 × 101 Half-step |
| C | Centum | 100 | 102 Base |
| D | Five Hundred | 500 | 5 × 102 Half-step |
| M | Mille | 1,000 | 103 Base |
5 Fundamental Rules of Roman Numerals
Unlike Arabic numbers, Roman numerals contain no zero symbol and follow strict positioning rules:
- Additive Principle: When symbols of equal value or larger value appear to the left of a smaller symbol, their values are added together (e.g.,
III = 3,VI = 6,MCL = 1150). - Subtractive Principle: When a smaller symbol is written directly before a larger symbol, the smaller value is subtracted from the larger one (e.g.,
IV = 5 - 1 = 4,CD = 500 - 100 = 400,CDXIV = 414). - Non-Repeatable Half-Step Symbols:
V(5),L(50), andD(500) can never be repeated or written to the left of a larger symbol. Expressions likeVXorLCare invalid. - Maximum 3 Consecutive Repetitions: Primary symbols (
I,X,C,M) can only be repeated up to three times consecutively (e.g.,III = 3,XXX = 30,MMM = 3000). WritingIIIIorXXXXis non-standard. - Subtractive Limits:
Ican only be subtracted fromV(4) orX(9).Xcan only be subtracted fromL(40) orC(90).Ccan only be subtracted fromD(400) orM(900).
Writing Large Numbers (> 3,999): Vinculum & Apostrophus
Because standard Roman numerals cannot repeat M more than three times, numbers equal to or greater than 4,000 require specialized notation systems:
1. Vinculum Notation (Overline 1,000x Multiplier)
The Vinculum system uses a horizontal bar written above a Roman numeral to multiply its value by 1,000. In digital text entry, an underscore prefix (e.g., _V) represents an overline:
| Standard Symbol | Base Value | Vinculum Overline (Converter Input) | Multiplied Value (× 1,000) |
|---|---|---|---|
| I | 1 | _I | 1,000 |
| V | 5 | _V | 5,000 |
| X | 10 | _X | 10,000 |
| L | 50 | _L | 50,000 |
| C | 100 | _C | 100,000 |
| D | 500 | _D | 500,000 |
| M | 1,000 | _M | 1,000,000 |
Using Vinculum notation allows this converter to calculate numbers up to 3,999,999.
2. Apostrophus Method
An older Renaissance system called Apostrophus used combinations of C and reversed † (C and ↄ) to represent thousands:
Iↄ= 500 |CIↄ= 1,000Iↄↄ= 5,000 |CCIↄↄ= 10,000Iↄↄↄ= 50,000 |CCCIↄↄↄ= 100,000
Step-by-Step Conversion Examples
Example 1: Convert Arabic 768 to Roman Numerals
Decompose 768 into place values:
768 = 700 + 60 + 8
Convert each place value separately:
- 700 =
DCC(500 + 100 + 100) - 60 =
LX(50 + 10) - 8 =
VIII(5 + 1 + 1 + 1)
Combine from left to right: 768 = DCCLXVIII
Example 2: Convert Roman MMMCCLXXVIII to Arabic
Group components from left to right:
- MMM = 3,000
- CC = 200
- LXX = 70
- VIII = 8
Sum all values: 3000 + 200 + 70 + 8 = 3278
Dates & Days of the Week in Roman Numerals
| Day of the Week | Roman Numeral Representation | Sample Date Format (March 4, 2025) |
|---|---|---|
| Monday | I | Full Roman: MMXXV / III / IV |
| Tuesday | II | Mixed Format: III / 4 / 2025 |
| Wednesday | III | ISO Dash: MMXXV - III - IV |
| Thursday | IV | European Mixed: 4 / III / 2025 |
| Friday | V | Cornerstone Inscription: IV.III.MMXXV |
| Saturday | VI | – |
| Sunday | VII | – |
To convert measurement units alongside numeric formats, check out our Conversion Calculator. For binary and hexadecimal computer number conversions, visit our Binary Calculator or Hex Calculator.
Frequently Asked Questions (FAQ)
Why is 4 sometimes written as IIII on clocks instead of IV?
Writing 4 as IIII on clock faces is a traditional watchmaker convention known as the “clockmaker’s 4.” It creates visual symmetry with VIII on the opposite side of the clock face and avoids confusion with upside-down VI (6).
Is there a Roman numeral for zero?
No. The ancient Romans did not have a numeral symbol for zero. When necessary, Latin scholars used words like nulla (meaning “none”) or the letter N to indicate an empty quantity.
How do I enter a Vinculum overline number in the online converter?
To enter a Vinculum number (multiplied by 1,000), place an underscore before the symbol. For example, type _V for 5,000, _X for 10,000, or _M for 1,000,000.
What is the largest number you can write with standard Roman numerals without an overline?
Without using a Vinculum overline, the largest standard Roman numeral is 3,999 (MMMCMXCIX), because M cannot be repeated more than three consecutive times.