How to Write Out Ordinal Numbers in Words in (US) American English, Rules, How to Spell Out, Exceptions, Comparison to (UK) British English.

1.1. Ordinal numbers - are those numbers defining a thing's position in a series:

• 1st - first - as a number, preceding all others in time, order, or importance;
  ex: They sat in the first row. He succeeded on his first attempt.
• 2nd - second - as a number, next to the first in place, time, or importance;
  ex: Our second option is to take a taxi. The second problem is the lack of global financing.
• 3rd - third - as a number, constituting number three in a sequence;
  ex: He came third in the competition. Our house is the third from the end on the left.
• 4th - fourth - as a number, constituting number four in a sequence;
  ex: He could do no better than finish fourth. Take the elevator to the fourth floor.
• 5th - fifth - as a number, constituting number five in a sequence;
  ex: May is the fifth month of the year. Coming in fifth place is better than finishing last.

1.2. Cardinal numbers - are those numbers denoting quantity, as opposed to ordinal numbers.

• 1 - one - as a number, the lowest cardinal number; half of two;
  ex: They have many daughters but only one son.
• 2 - two; - equivalent to the sum of one and one; one less than three;
  ex: The number that comes before three is two.

• 3 - three - equivalent to the sum of one and two; one more than two;
  ex: The bag contains three ounces of chocolate.
• 4 - four - equivalent to the product of two and two; one more than three;
  ex: Four people in five preferred this brand.
• 5 - five - equivalent to the sum of two and three; one more than four;
  ex: I am ten years old and my brother is five.

• First, to know how to write out a cardinal number in words it's important to know the name of the place where each digit is.
• For example, the number 12,345 has a 1 in the tens thousands place, a 2 in the thousands place, a 3 in the hundreds place, a 4 in the tens place, and a 5 in the units place.
• 12,345 in words is:
  ten thousand (10,000) + two thousand (2,000) + three hundred (300) + four tens (40) + five units (5) =
  ten thousand + two thousand + three hundred + forty + five =
  twelve thousand three hundred forty-five.

2.1. Useful notes / guidelines:

• 1: Note the hyphen (or the minus sign) in "twenty-three" above. Technically, it's correct to hyphenate all compound numbers from twenty-one, 21, to ninety-nine, 99. Using a hyphen also applies to ordinal numbers between 21st and 99th (notice the "st" and "th" after the cardinal numbers).
• 2: "And" placement - in (US) American English, do not use the word "and" after "hundred" or "thousand" (In British English, the word "and" is used after "hundred" or "thousand"). So it is "one hundred twenty-three" and not "one hundred and twenty-three", though you may hear a lot of people using the last, informally. The word "and" is used only when expressing the decimal points in decimal numbers.
• 3: With figures of four or more digits, use commas, ex: 1,154, 12,345.
• 4: When writing out numbers above 999, in American English, do not use commas. Incorrect (it is correct in British English): one thousand, one hundred fifty-four (1,154). Correct: one thousand one hundred fifty-four (1,154).

Most ordinal numbers end in "th", so just add "th" to the end of the cardinal number:

• four → 4th - fourth
• six → 6th - sixth
• seven → 7th - seventh

• ten → 10th - tenth
• eleven → 11th - eleventh
• nineteen → 19th - nineteenth
• one hundred → 100th - (one) hundredth
• one thousand → 1,000th - (one) thousandth
• one million → 1,000,000th - (one) millionth

3.1. Exceptions:

• one → first - 1st
• two → second - 2nd
• three → third - 3rd
• five → fifth - 5th
• eight → eighth - 8th
• nine → ninth - 9th
• twelve → twelfth - 12th
• twenty → twentieth - 20th
• thirty → thirtieth - 30th
• forty → fortieth - 40th
• fifty → fiftieth - 50th
• sixty → sixtieth - 60th
• seventy → seventieth - 70th
• eighty → eightieth - 80th
• ninety → ninetieth - 90th

3.2. In compound ordinal numbers only the last digit is written as an ordinal:

• 27 = twenty-seven → 27th = twenty-seventh
• 123 = one hundred twenty-three → 123rd = one hundred twenty-third
• 1,213,498 = one million two hundred thirteen thousand four hundred ninety-eight → 1,213,498th = one million two hundred thirteen thousand four hundred ninety-eighth

3.3. When expressing ordinal numbers as figures, the last two letters of the written word are added to the ordinal number written in digits:

• first - 1st
• second - 2nd
• third - 3rd

• fourth - 4th
• thirty-fourth - 34th
• five thousand four hundred thirty-ninth - 5,439th

Here there are the main ordinal numbers, listed in ascending order, together with their corresponding cardinal numbers:

• cardinal: 1, one → ordinal: 1st, first;
• cardinal: 2, two → ordinal: 2nd, second;
• cardinal: 3, three → ordinal: 3rd, third;
• cardinal: 4, four → ordinal: 4th, fourth;
• cardinal: 5, five → ordinal: 5th, fifth;
• cardinal: 6, six → ordinal: 6th, sixth;
• cardinal: 7, seven → ordinal: 7th, seventh;
• cardinal: 8, eight → ordinal: 8th, eighth;
• cardinal: 9, nine → ordinal: 9th, ninth;
• cardinal: 10, ten → ordinal: 10th, tenth;
• cardinal: 11, eleven → ordinal: 11th, eleventh;
• cardinal: 12, twelve → ordinal: 12th, twelfth;
• cardinal: 13, thirteen → ordinal: thirteenth;
• cardinal: 14, fourteen → ordinal: 14th, fourteenth;
• cardinal: 15, fifteen → ordinal: 15th, fifteenth;
• cardinal: 16, sixteen → ordinal: 16th, sixteenth;
• cardinal: 17, seventeen → ordinal: 17th, seventeenth;
• cardinal: 18, eighteen → ordinal: 18th, eighteenth;
• cardinal: 19, nineteen → ordinal: 19th, nineteenth;
• cardinal: 20, twenty → ordinal: 20th, twentieth;
• cardinal: 21, twenty one → ordinal: 21st, twenty first;
• cardinal: 22, twenty two → ordinal: 22nd, twenty second;
• cardinal: 23, twenty three → ordinal: 23rd, twenty third →
• cardinal: 24, twenty four → ordinal: 24th, twenty fourth;
• cardinal: 25, twenty five → ordinal: 25th, twenty fifth;
• cardinal: 26, twenty six → ordinal: 26th, twenty sixth;
• cardinal: 27, twenty seven → ordinal: 27th, twenty seventh;
• cardinal: 28, twenty eight → ordinal: 28th, twenty eighth;
• cardinal: 29, twenty nine → ordinal masculin: 29th, twenty ninth;
• cardinal: 30, thirty → ordinal: 30th, thirtieth;
• cardinal: 31, thirty one → ordinal: 31st, thirty first;
• cardinal: 40, forty → ordinal: 40th, fortieth;
• cardinal: 50, fifty → ordinal: 50th, fiftieth;
• cardinal: 60, sixty → ordinal: 60th, sixtieth;
• cardinal: 70, seventy → ordinal: 70th, seventieth;

• cardinal: 80, eighty → ordinal: 80th, eightieth;
• cardinal: 90, ninety → ordinal: 90th, ninetieth;
• cardinal: 100, one hundred → ordinal: 100th, (one) hundredth;
• cardinal: 101, one hundred one → ordinal: 101st, one hundred first;
• cardinal: 112, one hundred twelve → ordinal: 112th, one hundred twelfth;
• cardinal: 200, two hundred → ordinal: 200th, two hundredth;
• cardinal: 300, three hundred → ordinal: 300th, three hundredth;
• cardinal: 1,000, one thousand → ordinal: 1,000th, (one) thousandth;
• cardinal: 1,001, one thousand one → ordinal: 1,001st, one thousand first;
• cardinal: 2,000, two thousand → ordinal: 2,000th, two thousandth;
• cardinal: 3,000, three thousand → ordinal: 3,000th, three thousandth;
• cardinal: 12,000, twelve thousand → ordinal: 12,000th, twelve thousandth;
• cardinal: 20,000, twenty thousand → ordinal: 20,000th, twenty thousandth;
• cardinal: 20,001, twenty thousand one → ordinal: 20,001st, twenty thousand first;
• cardinal: 50,000, fifty thousand → ordinal: 50,000th, fifty thousandth;
• cardinal: 100,000, one hundred thousand → ordinal: 100,000th, one hundred thousandth;
• cardinal: 500,000, five hundred thousand → ordinal: 500,000th, five hundred thousandth;
• cardinal: 1,000,000, one million → ordinal: 1,000,000th, (one) millionth;
• cardinal: 2,000,000, two million → ordinal: 2,000,000th, two millionth;
• cardinal: 1,000,000,000, one billion → ordinal: 1,000,000th, (one) billionth;
• cardinal: 1,000,000,000,000, one trillion → ordinal: 1,000,000,000th, (one) trillionth;
• cardinal: 1,000,000,000,000,000, one quadrillion → ordinal: 1,000,000,000,000th, (one) quadrillionth;
• cardinal: 1,000,000,000,000,000,000, one quintillion → ordinal: 1,000,000,000,000,000th, one quintillionth;
• cardinal: 1,000,000,000,000,000,000,000, one sextillion → ordinal: 1,000,000,000,000,000,000th, one sextillionth; etc...

• Since it's ok to write ordinal numbers in figures (1st, 2nd, 3rd, ...) in informal writing to friends, colleagues, etc, we need to write them in words in formal writing - business, job applications, etc.
• When beginning a sentence, "Twentieth year of her life... " and not "20th year of her life...".
• The Chicago Manual of Style recommends spelling out the numbers zero through one hundred and using figures thereafter - except for whole numbers used in combination with hundred, thousand, hundred thousand, million, billion, and beyond (e.g., two hundredth; twenty-eight thousandth; three hundred thousandth; one millionth, one hundred millionth).

» Calculator: convert ordinal numbers to (US) American English words, write them out using letters instead of numerals