Roman Numeral Converter
Convert between Roman and Decimal numbers instantly.
Conversion Result
The History and Rules of Roman Numerals
Roman numerals originated in ancient Rome and remained the dominant number system in Europe until the late Middle Ages. They are based on a combination of letters from the Latin alphabet, each with a specific integer value. This system is additive and subtractive, allowing for a compact representation of numbers.
Core Symbols
- I = 1
- V = 5
- X = 10
- L = 50
- C = 100
- D = 500
- M = 1000
Conversion Rules
To convert Roman numerals, you read them from left to right.
- Addition: When a symbol of equal or lesser value follows a symbol of greater value, their values are added. For example,
VI= 5 + 1 = 6, andLXX= 50 + 10 + 10 = 70. - Subtraction: When a symbol of smaller value precedes a symbol of larger value, the smaller value is subtracted from the larger one. This rule applies only to specific pairs:
IV(4),IX(9),XL(40),XC(90),CD(400), andCM(900). - Repetition: A symbol can be repeated up to three times to multiply its value (e.g.,
III= 3,XXX= 30). The symbols V, L, and D are never repeated.
Frequently Asked Questions
How do you convert difficult numbers like 1999?
You break the number down into its constituent parts based on the rules. For 1999: 1000 is M, 900 is CM, 90 is XC, and 9 is IX. Combining these gives MCMXCIX.
What is the largest number you can write?
Using the standard symbols, the largest number is 3999 (MMMCMXCIX). Historically, a line (vinculum) over a numeral multiplied its value by 1,000, allowing for larger numbers, but this is not part of the common modern standard.
Why is 'IIII' sometimes used on clocks instead of 'IV'?
This is a tradition in clockmaking known as the "watchmaker's four." Reasons vary, but it's often done for visual symmetry on the clock face, balancing with the VIII on the other side. While historically used, in standard Roman numeral notation, 'IIII' is considered incorrect.
