Convert Roman (roman) to Decimal (decimal) instantly. Convert Roman numerals to numbers.
| Unit | Name | Value |
|---|---|---|
| decimal | Decimal (1, 2, 3...) | — |
Core Roman numeral values:
Subtractive rule: smaller numeral before larger means subtraction (IV = 4, IX = 9, XL = 40).
Complete reference from 1 to 2026 with subtractive notation highlights
| Roman Numeral | Decimal Value | Notes |
|---|---|---|
| I | 1 | I |
| II | 2 | II |
| III | 3 | III |
| IV | 4 | IV — subtractive |
| V | 5 | V |
| VI | 6 | VI |
| VII | 7 | VII |
| VIII | 8 | VIII |
| IX | 9 | IX — subtractive |
| X | 10 | X |
| XI | 11 | XI |
| XII | 12 | XII |
| XIII | 13 | XIII |
| XIV | 14 | XIV |
| XV | 15 | XV |
| XX | 20 | XX |
| XXX | 30 | XXX |
| XL | 40 | XL — subtractive |
| L | 50 | L |
| XC | 90 | XC — subtractive |
| C | 100 | C |
| CD | 400 | CD — subtractive |
| D | 500 | D |
| CM | 900 | CM — subtractive |
| M | 1000 | M |
| MCMXCIX | 1999 | Most complex 4-digit |
| MM | 2000 | MM |
| MMXXIV | 2024 | Recent year |
| MMXXV | 2025 | Recent year |
| MMXXVI | 2026 | Current year |
Add each symbol's value. If a smaller value comes before a larger one, subtract it instead of adding: IV = 5−1 = 4, IX = 10−1 = 9, XL = 50−10 = 40, XC = 100−10 = 90, CD = 500−100 = 400, CM = 1000−100 = 900.
Break the numeral into groups: MCMXCIX → M(1000) + CM(900) + XC(90) + IX(9) = 1999.
IV, IX, XL, XC, CD, CM — memorize these and everything else is just addition.
Reads dates on monuments, buildings, coins, and historical documents in Roman numerals.
Decodes copyright years in movie credits — studios traditionally use Roman numerals.
Interprets Roman numerals in textbook chapter numbering, outline formatting, and exam questions.
Reads Roman numeral clock faces, which use I–XII for hours.
Interprets Roman numeral citations in law (Article I, Section II, Clause III).
Uses Roman numerals for Super Bowl, Olympics, and World Series numbering (e.g. Super Bowl LVIII).
Roman numerals were developed by the ancient Romans and used throughout the Roman Empire from at least the 3rd century BCE. The system evolved from earlier Etruscan numerals and tally marks — I representing one finger, V the open hand (5), and X two hands crossed (10).
The subtractive notation (IV instead of IIII, IX instead of VIIII) became widespread in medieval Europe, though ancient Roman inscriptions often used additive forms. The system was the dominant notation in Western Europe until Arabic numerals gradually replaced it between the 11th and 15th centuries.
Interesting fact: The Roman numeral system has no zero and no easy way to represent large numbers — one reason why Arabic numerals (which include zero and place value) were eventually adopted for mathematics and commerce. Roman numerals survive today primarily in ceremonial and stylistic contexts.
The decimal (base-10) number system, also called the Hindu-Arabic numeral system, was developed in India around the 6th century CE and transmitted to Europe via Arabic mathematicians in the 9th–12th centuries. Its key innovation — positional notation with a zero — made arithmetic vastly more efficient than any previous system.
Fibonacci's Liber Abaci (1202) was instrumental in popularizing Arabic numerals in Europe, demonstrating their superiority for commerce and calculation. By the 16th century, decimal numerals had largely replaced Roman numerals for mathematical and commercial use.
Interesting fact: The word 'decimal' comes from the Latin decimus (tenth). Every culture that developed mathematics independently chose base-10 as their primary number system — most likely because humans have 10 fingers.
Converting Roman numerals to decimal is useful for reading historical dates, decoding film copyright years, interpreting event numbering (Super Bowl LVIII = 58), and understanding chapter or section numbering in books and legal documents.
The core rule: read left to right, adding each symbol's value. The only exception is the six subtractive pairs: IV(4), IX(9), XL(40), XC(90), CD(400), CM(900). When you see a smaller value before a larger one, subtract instead of add.
Roman numerals represent integers from 1 to 3,999. The system has no zero, no negative numbers, and no fractions.