## Ordinal Numbers

Teaching ESL students how to form ordinal numbers is an important math basic. Ordinal numbers are numbers used for indicating order. The majority of ordinal numbers are formed by affixing the *-th* suffix onto the cardinal number:

- 1st – first*
- 2nd – second*
- 3rd – third*
- 4th – fourth
- 5th – fifth*
- 6th – sixth
- 7th – seventh
- 8th – eighth
- 9th – ninth*
- 10th – tenth
- 11th – eleventh
- 12th – twelfth*
- 13th – thirteenth
- 14th – fourteenth
- 15th – fifteenth
- 16th – sixteenth
- 17th – seventeenth
- 18th – eighteenth
- 19th – nineteenth

However, note that first (1st), second (2nd), third (3rd), and fifth (5th) are irregular: first (1st) and second (2nd) must simply be memorized, but third (3rd) and fifth (5th) are related to the spelling and pronunciation changes of the cardinal numbers thirteen (13) and thirty (30) and fifteen (15) and fifty (50). Also point out the slight spelling change in ninth (9th) and twelfth (12th).

For multiples of ten, a final *y* changes to an *ie* and then the *-eth* suffix is affixed to the end of the number:

- 20th – twentieth
- 30th – thirtieth
- 40th – fortieth
- 50th – fiftieth
- 60th – sixtieth
- 70th – seventieth
- 80th – eightieth
- 90th – ninetieth

All other numbers above twenty follow the *-th* suffix rule in combination with the rules for the first nineteen numbers and the multiples of ten. For example:

- 21st – twenty-first
- 100th – one hundredth
- 101st – one hundred and first OR one hundred and oneth*
- 110th – one hundred and tenth
- 1,000th – one thousandth
- 1,111th – one thousand one hundred and eleventh
- 1,000,000 – one millionth

*The use of *oneth* in higher ordinal numbers is nonstandard but often used by native English speakers.

## Decimals

Next introduce the words for the decimals:

- 0.X – tenth(s)
- 0.0X – hundredth(s)
- 0.00X – thousandth(s)
- 0.000X – ten thousandth(s)
- 0.0000X – hundred thousandth(s)
- 0.00000X – millionth(s)

All decimals follow the singular-plural system for English nouns in that the number is spoken as the digit followed by the name of the decimal with any decimal larger than one taking the plural *–s* marker. A period is placed between the whole number and the decimal. For example:

- 0.1 – one tenth
- 0.2 – two tenths
- 0.01 – one hundredth, one one-hundredth
- 0.33 – thirty-three hundredths
- 0.001 – one thousandths, one one thousandth
- 0.654321 – six hundred fifty-four thousand three hundred twenty-one millionths

Decimals may also be spoken as whole number-point-digits. Zeros are spoken as *zero* or *oh*. For example:

- 0.1 – point one, zero point one, oh point one
- 1.25 – one point two five
- 6.425 – six point four two five
- 2.1368 two point one three six eight
- 1.057 – one point oh five seven
- 4.0098 – four point zero zero nine eight

## Fractions

Finally teach the ESL students how to form fractions in English. The numerator (the top number) is spoken as a cardinal number and the denominator (the bottom number) as an ordinal number. However, *half* is used in place of *second* and sometimes *quarter* in place of *fourth*. For fractions in which the numerator is larger than one, the denominator takes the plural *-s* suffix. English fractions are also written with a hyphen between the numerator and denominator. For example:

- 1/2 – one-half
- 1/3 – one-third
- 2/3 – two-thirds
- 1/4 – one-fourth, one-quarter
- 4/5 – four-fifths
- 99/100 – ninety-nine one hundredths, ninety-nine hundredths

Fractions may also be spoken as cardinal number-over-cardinal number. For example:

- 1/2 – one over two
- 1/3 – one over three
- 2/3 – two over three
- 1/4 – one over four
- 4/5 – four over five
- 99/100 – ninety-nine over one hundred

For a printable study sheet of the English cardinal numbers, please download English Ordinal Numbers, Decimals, and Fractions Study Sheet.

## This post is part of the series: English Numbers

- ESL Lesson Plans: Cardinal Numbers in English
- ESL Lesson Plans: Decimals, Fractions, and Ordinal Numbers in English