Latin numerals

One
Two
Three
Four
Five
Six
Seven
Eight
Nine
Ten
Eleven
Twelve
Thirteen
Fourteen
Fifteen
Sixteen
Seventeen
Eighteen
Nineteen
Twenty

Thirty

Forty

Fifty

Sixty

Seventy

Eighty

Ninety

One hundred

One thousand

I
II       
III
IV
V
VI
VII
VIII
IX
X
XI
XII
XIII
XIV
XV
XVI
XVII
XVIII
XIX
XX

XXX

XL   

L

LX

LXX

LXXX

XC

C

M    

Cardinal numbers

unus
duo
tres
quattuor
quinque
sex
septem
octo
novem
decem
undecim
duodecim
tredecim
quattuordecim
quindecim
sedecim
septendecim
duedeveginti
uneviginti
viginti

triginta

quadraginta

quinquaginta

sexaginta

septuaginta

octoginta

nonaginta

centum

mille

Latin numerals

Latin or Roman numerals work by repeating and combining the following digits:  I, V, X,  L and C.

When a digit  is repeated more than once, it is added.  So II is 1+1 and III 1+1+1

A smaller digit is added to a larger digit when it occurs before the larger, so VIII is 5+1+1+1. However, where a smaller digit  occurs after a larger digit it is subtracted, so IX is 10 - 1.

So, for example 28 could be XXVIII 10+10+5+1+1+1 or XX1X 10+10+10-1.

There are a few further rules but the above cover the majority of situations.