Roman numerals

Both directions, with the rules underneath. Standard modern form, I to MMMCMXCIX.

Written 28 September 2026.

Number to Roman numeral

Number

A whole number from 1 to 3999.

Roman numeral

In words:

Roman numeral to number

Roman numeral

Lowercase is fine. Nonstandard spellings such as IIII are read and corrected.

Number

In words:

Writing a whole date? Roman numeral dates converts one in any order and reads one back, with every reading it could have.

The seven letters

Every Roman numeral is built from these seven. Read left to right, adding as you go. When a smaller letter sits in front of a larger one, it is taken away instead.

The seven Roman numeral letters
Letter	Value
I	1
V	5
X	10
L	50
C	100
D	500
M	1,000

The six subtractive pairs

These are the only subtractions the standard form allows. A letter is only ever taken from the next two values up, which is why 99 is XCIX and not IC. The mistakes this rule catches.

Every subtraction a standard Roman numeral can contain
Pair	Value	How it reads
IV	4	I before V takes one from five
IX	9	I before X takes one from ten
XL	40	X before L takes ten from fifty
XC	90	X before C takes ten from a hundred
CD	400	C before D takes a hundred from five hundred
CM	900	C before M takes a hundred from a thousand

Numerals worth a second look

4 is IV. The first subtractive numeral. IIII appears on clock faces but IV is the standard form.
9 is IX. I before X, taking one from ten.
40 is XL. X before L. XXXX is not the standard form.
49 is XLIX. Two subtractions in one numeral: XL for forty and IX for nine.
99 is XCIX. A common trap. It is XCIX, not IC — a subtraction only ever uses the next two letters up.
1999 is MCMXCIX. Three subtractive pairs in one numeral: CM, XC and IX. The shortcut MIM is not the standard form, because I is only ever taken from V or X.
3999 is MMMCMXCIX. The largest number with a standard Roman numeral. Above this the system needs an overline.

One to twenty

1 I
2 II
3 III
4 IV
5 V
6 VI
7 VII
8 VIII
9 IX
10 X
11 XI
12 XII
13 XIII
14 XIV
15 XV
16 XVI
17 XVII
18 XVIII
19 XIX
20 XX

Reference tables

Years people look up

The convention used here. Roman numerals have never had one agreed form. Clock faces use IIII where the converter uses IV, and medieval scribes wrote IIXX for eighteen. The converter follows the standard modern form, from I to MMMCMXCIX. Above that the system needs an overline to multiply by a thousand, which is not used here.