Roman numerals
This numeric system originated in ancient Rome. Numbers in the Roman system are represented by combinations of letters from the Latin alphabet.
They are based on the following seven symbols, each with a fixed integer value:
| Symbol |
Value |
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1000 |
The digits we normally use today, 0–9, are called Arabic numerals.
Basic numbers look like this:
1 - I
2 - II
3 - III
4 - IV
5 - V
6 - VI
7 - VII
8 - VIII
9 - IX
10 - X
15 - XV
20 - XX
40 - XL
50 - L
60 - LX
80 - LXXX
100 - C
200 - CC
300 - CCC
400 - CD
500 - D
700 - DCC
900 - CM
How to form a number
When symbols are written from a greater value to a smaller or equal value, their values are added:
| Roman numeral |
Decomposition |
Result |
| II |
|
2 |
| III |
|
3 |
| LXXX |
| L + X + X + X |
| 50 + 10 + 10 + 10 |
|
80 |
| MDCXXI |
| M + D + C + X + X + I |
| 1000 + 500 + 100 + 10 + 10 + 1 |
|
1621 |
In some cases, a smaller symbol placed before a larger symbol is subtracted. The standard combinations are IV, IX, XL, XC, CD and CM:
| Roman numeral |
Decomposition |
Result |
| IV |
|
4 |
| XC |
|
90 |
The symbols I, X, C and M can be repeated up to three times in succession. The symbols V, L and D are not repeated.
How to form a Roman numeral
To convert an Arabic numeral to a Roman numeral, write the number in expanded form and then replace each part with the correct Roman symbols:
| Arabic numeral |
Decomposition |
Result |
| 1511 |
| 1000 + 500 + 10 + 1 |
| M + D + X + I |
|
MDXI |
| 969 |
| 900 + 60 + 9 |
| CM + LX + IX |
|
CMLXIX |
