Let's
start with the good news: there is (almost) no difference between the way that
we write numbers in Spanish and the way we write them in English. The bad news
is that when we use numbers in conversation, they definitely aren't pronounced
the same way. But whether you've picked it up from "Sesame Street" or
"Dora the Explorer" you probably already know at least a handful of
Spanish numbers. Keep reading to learn more.
Cardinal Numbers
A "cardinal number" is just a fancy term for a numbers
we use in counting things (or indicating times, dates, or ages).
Let's take a trip through the Spanish cardinal numbers from
cero (0) to un trilión (1,000,000,000,000,000,000)
noticing some interesting quirks along the way.
Fun Fact: Cinco is the only Spanish number
with the same number of letters as the number it represents.
The first 10 numbers (as well as zero)
all have unique names:

cero 
zero 
0 

uno 
one 
1 

dos 
two 
2 

tres 
three 
3 

cuatro 
four 
4 

cinco 
five 
5 

seis 
six 
6 

siete 
seven 
7 

ocho 
eight 
8 

nueve 
nine 
9 

diez 
ten 
10 
The next five also have unique names:

once 
eleven 
11 

doce 
twelve 
12 

trece 
thirteen 
13 

catorce 
fourteen 
14 

quince 
fifteen 
15 
Note: There are two acceptable options for writing the
numbers 16 through 19. The "oldschool" way is to simply say "ten
and six," "ten and seven," etc. The newer method is to combine
those words into one word. At that point the "z" in diez becomes a "c" and the "y" becomes an "i." Both versions
are pronounced the same way. The shorter, combined word is preferred nowadays.
After that the numbers come in combinations. You are literally saying
"ten and six," "ten and seven," "ten and eight,"
etc.:

dieciséis
/ diez y seis 
sixteen 
16 

diecisiete / diez
y siete 
seventeen 
17 

dieciocho / diez y ocho 
eighteen 
18 

diecinueve
/ diez y nueve 
nineteen 
19 
Veinte means "twenty" and from that point on the pattern is very similar to
sixteen through nineteen; you are literally saying "twenty and one,"
"twenty and two," etc.:
Note: Once again it is also preferable to condense these
numbers down to one word by replacing the trailing "e"
and the "y" with an "i." Twenty two, twenty three, and twenty
six will also need an additional accent mark.

veinte 
twenty 
20 

veintiuno / veinte y uno 
twentyone 
21 

veintidós / veinte y dos 
twentytwo 
22 

veintitrés / veinte y tres 
twentythree 
23 

veinticuatro / veinte y cuatro 
twentyfour 
24 

veinticinco / veinte y cinco 
twentyfive 
25 

veintiséis / veinte y seis 
twentysix 
26 

veintisiete / veinte y siete 
twentyseven 
27 

veintiocho / veinte y ocho 
twentyeight 
28 

veintinueve / veinte y nueve 
twentynine 
29 
After veinte comes treinta and the same pattern is followed:
Note: After the twenties we no longer condense our numbers
into one word.

treinta 
thirty 
30 

treinta y uno 
thirtyone 
31 

treinta y dos 
thirtytwo 
32 

treinta y tres 
thirtythree 
33 

etc. 
etc. 

All of the numbers in the forties, fifties, sixties, seventies,
eighties, and nineties work the same way as in the thirties:

cuarenta 
forty 
40 

cincuenta 
fifty 
50 

cincuenta y uno 
fiftyone 
51 

sesenta 
sixty 
60 

setenta 
seventy 
70 

ochenta 
eighty 
80 

ochenta y cinco 
eightyfive 
85 

noventa 
ninety 
90 
Note: The plural of cien is cientos (not cienes.)
Technically ciento means "one hundred" in Spanish, but its shortened form, cien, is preferred when there are exactly 100 of something:

cien 
one hundred 
100 

ciento uno 
one hundred one 
101 

ciento dos 
one hundred two 
102 

ciento tres 
one hundred three 
103 

etc. 
etc. 

You may have noticed there is no longer any y." This is
because the "y" is only used to separate the 10's place from the 1's
place. If there is nothing in the 10's place, we don't use "y."

ciento diez 
one hundred ten 
110 

ciento veinte 
one hundred twenty 
120 

ciento veintiuno 
one hundred twentyone 
121 

ciento treinta y cinco 
one hundred thirty five 
135 

etc. 
etc. 

Ciento is followed by:

doscientos 
two hundred 
200 

doscientos cincuenta 
two hundred fifty 
250 

trescientos 
three hundred 
300 

cuatrocientos 
four hundred 
400 

quinientos 
five hundred 
500 

seiscientos 
six hundred 
600 

setecientos 
seven hundred 
700 

ochocientos 
eight hundred 
800 

novecientos 
nine hundred 
900 
"One thousand" in Spanish is mil. And we don't
un mil; it's simply mil:

mil 
one thousand 
1.000 

mil quinientos 
one thousand five hundred 
1.500 

dos mil 
two thousand 
2.000 

tres mil 
three thousand 
3.000 

etc. 
etc. 

After the thousands comes the 10s and 100s of thousands:
Note: In compound numbers, Use ciento if the number that follows is smaller than 100. Use cien if the number that follows is larger than 100.

diez mil 
ten thousand 
10.000 

cien mil 
one hundred thousand 
100.000 

ciento treinta mil 
one hundred thirty thousand 
130.000 

doscientos mil 
two hundred thousand 
200.000 

trescientos mil 
three hundred thousand 
300.000 

etc. 
etc. 

Next, a thousand
thousand is a million or un millón. When we move from one million, millón becomes millones:

un millón 
one million 
1.000.000 

un millón doscientos mil 
one million two hundred thousand 
1.200.000 

dos millones 
two million 
2.000.000 

tres millones 
three million 
3.000.000 

etc. 
etc. 

Note: This is not actually so much of a difference in languages
as it is a difference in ways of counting very large numbers. Historically there
is some disagreement even between Englishspeaking countries as to what exactly
"billion" represents.
Bonus: see Long and short scales
Now things get a little weird. Adding three zeros to a million in English
gets us to a billion. But in Spanish it's a mil millón, or
a thousand million. This throws the rest of the chart out of synch with what
we might expect as well:

mil millones 
one billion 
1.000.000.000 

dos mil millones 
two billion 
2.000.000.000 

un billón 
one trillion 
10^{12} 

mil billones 
one quadrillion 
10^{15} 

un trillón 
one quintillion 
10^{18} 
Cardinal Numbers as Adjectives
If
you're simply counting numbers (like in "Hide and Seek" while your friends are
hiding) the list above is accurate. However, much of the time when we use a number
we follow it up with a noun, e.g. "six cars," "24 tables,"
"38 houses," etc. When we do this we're actually using the number as
an adjective and some interesting things need to happen.
First of all uno
gets shortened to un when it comes before a masculine noun, and likewise
numbers ending in "uno" are shortened to "ún" (note
the accent mark). Ciento is also shortened to cien when
(and only when) we're dealing with exactly 100 of something. For example:
cien coches
ciento tres coches
Secondly,
as with other adjectives, we need to make our numbers agree in gender with
the nouns that they modify. However, this only happens with numbers ending in
"uno" and words ending in "ientos" (all of the "hundreds"
words from 200 to 900). For example:
masculine: 
feminine: 
un
coche 
una casa 
veintiún coches 
veintiuna casas 
cien coches 
cien casas 
quinientos
coches 
quinientas
casas 
Every part of a number that can agree with the
gender of the noun should agree. For example 654,321 tables would be written out
as "seiscientas cincuenta y cuatro mil trescientas veintiuna mesas."
Decimal Points and Commas
You may have noticed the
strange looking decimal points in the right hand column above. This is not a typo.
The majority of Spanishspeaking countries do the opposite of Englishspeaking
countries when it comes to decimal points and grouping thousands: commas are used
for decimal points and periods are used to separate the groups of zeros. The number
"21.7" would be written "21,7" in Spanish and would be read
"veintiuno punto siete."
Ordinal Numbers
While we use cardinal numbers to count things, we use "ordinal numbers" to put things in order
(such as the order in which runners finish a race). Here are the Spanish ordinal numbers :

primero 
first 

segundo 
second 

tercero 
third 

cuarto 
fourth 

quinto 
fifth 

sexto 
sixth 

séptimo 
seventh 

octavo 
eighth 

noveno 
ninth 

décimo 
tenth 

onceavo / undécimo / decimoprimero 
eleventh 

doceavo / duodécimo / decimosegundo 
twelfth 

décimo tercero 
thirteenth 

décimo cuarto 
fourteenth 

etc. 
etc. 

 
 

vigésimo 
twentieth 

vigésimo primero 
twentyfirst 

vigésimo segundo 
twentysecond 

etc. 
etc. 

 
 

trigésimo 
thirtieth 

cuadragésimo 
fortieth 

quincuagésimo 
fiftieth 

sexagésimo 
sixtieth 

septuagésimo 
seventieth 

octogésimo 
eightieth 

nonagésimo 
ninetieth 

centésimo 
hundredth 

milésimo 
thousandth 

último 
last 
 When used as adjectives, all of the ordinals agree in gender
with the noun they modify, therefore "o" endings change to "a"
with feminine nouns. For example: la segunda casa, su tercera
novia, mi última tarea.
 The ordinals primero and tercero are shortened to primer and tercer when used with masculine nouns. For example; en primer lugar, en
tercer grado. This is only true of primero and tercero.
 When an ordinal prefix ending in "imo" is combined with "octavo" one of the o's is dropped to avoid repeating the same sound, e.g. "decimoctavo."
 Ordinals are not typically used with dates; use cardinal numbers instead: "Hoy es el quince de enero."
 We often use a sort of shorthand abbreviation for ordinals in English — 1st, 2nd, 3rd, etc. We can do something similar in Spanish — 1º, 2º,
3º, etc. (or 1ª, 2ª, 3ª, etc. if feminine)
Fractions
We
express Spanish fractions the following way:

un entero 
a whole (1/1) 

una mitad 
one
half (1/2) 

dos tercios 
two
thirds (2/3) 

tres cuartos 
three quarters (3/4) 

cuatro quintos 
four
fifths (4/5) 

cinco sextos 
five sixths (5/6) 

seis séptimos 
six sevenths (6/7) 

siete octavos 
seven eighths (7/8) 

ocho novenos 
eight ninths (8/9) 

nueve décimos 
nine tenths (9/10) 

nueve centésimos 
nine hundredths (9/100) 

nueve milésimos 
nine thousandths (9/1000) 

etc. 
etc. 
From un cuarto on we're using the same words as we did for the ordinals.
Multiples
Note: Multiples can also have masculine and feminine forms: cuádruplo, cuádrupla.
We use "multiplicatives" to make multiples out of a number. Spanish multiples are similar to the English:

doble 
double 

triple 
triple 

cuádruple 
quadruple 

quíntuple 
quintuple 

séxtuple 
sextuple 

séptuple 
septuple 

óctuple 
octuple 

nónuplo 
nonuple 

décuplo 
decuple 

etc. 
etc. 
Percentages
Precentages are written the same way in Spanish as they are in English. The word "percent" is por ciento in Spanish.

6 por ciento 
6 percent (6%) 

75 por ciento 
75 percent (75%) 

99 por ciento 
99 percent (99%) 
Fun Numbers Facts
 When writing
checks in Spanish it is acceptable (and a good idea) to write "un mil"
rather than the grammatically correct "mil" to ensure that no one alters
the check amount.
 Writing "two or three" in Spanish looks like
this, "2 o 3," and could possibly be confused with "203."
Because of this the "or" is somtimes accented to avoid confusion: "2 ó
3." (As handwriting is being replaced by technology, the need to do this is diminishing.)