- -st is used with numbers ending in 1 (e.g. 1st, pronounced first)
- -nd is used with numbers ending in 2 (e.g. 92nd, pronounced ninety-second)
- -rd is used with numbers ending in 3 (e.g. 33rd, pronounced thirty-third)
- As an exception to the above rules, all the "teen" numbers ending with 11, 12 or 13 use -th (e.g. 11th, pronounced eleventh, 112th, pronounced one hundred [and] twelfth)
- -th is used for all other numbers (e.g. 9th, pronounced ninth).
In the 19th century, under French influence, these indicators were often written as superscripts (e.g. 2nd, 34th), especially in British English. During most of the 20th century, formatting them on the baseline was favored. The 16th edition of The Chicago Manual of Style states: "The letters in ordinal numbers should not appear as superscripts (e.g., 122nd not 122nd)", as do the Bluebook and style guides by the Council of Science Editors, Microsoft, and Yahoo!. Two problems are that superscripts are used "most often in citations" and are "tiny and hard to read". Some word processors format ordinal indicators as superscripts by default (e.g. Microsoft Word). Style guide author Jack Lynch (Rutgers) recommends turning off automatic superscripting of ordinals in MS Word, because "no professionally printed books use superscripts."
The suffixes -er (e.g. 1er – premier), -re (e.g. 1re – première), and -e (e.g. 2e – deuxième). These indicators use superscript formatting whenever it is available. Alternatively, the suffix -ème is a common mistake in place of -e (e.g. 2ème – deuxième).
Unlike other Germanic languages, Dutch is similar to English in this respect: the French layout with -e used to be popular, but the recent spelling changes now prescribe the suffix -e. Optionally -ste and -de may be used, but this is more complex and nowadays less used: 1ste (eerste), 2de (tweede), 4de (vierde), 20ste (twintigste), etc.
Croatian, Czech, Danish, Estonian, Faroese, German, Hungarian, Icelandic, Latvian, Norwegian, Polish, Slovak, Slovene, Serbian, Turkish 
A period or full stop is written after the numeral. The same usage, apparently borrowed from German, is now a standard in Polish, where it replaced the superscript of the last phoneme (following complex declension and gender patterns, e.g., 1szy, 7ma, 24te, 100ny).
Galician, Italian, Portuguese, and Spanish 
The suffixes -o and -a are appended to the numeral depending on whether the number's grammatical gender is masculine or feminine respectively. As with French, these signs are preferably superscripted but, in contrast, they are often underlined as well. Some character sets provide characters specifically for use as ordinal indicators in these languages: º and ª (in Unicode U+00BA and U+00AA). The masculine ordinal indicator U+00BA (º) is often confused with the degree sign U+00B0 (°), which looks very similar in many fonts and is available on Italian and Spanish keyboard layout. The degree sign is a uniform circle and is never underlined, while the letter o may be oval or elliptical and have a varying stroke width. The letter o may also be underlined.
In Spanish, using the two final letters of the word as it is spelled is not allowed, except in the cases of primer (an apocope of primero) before singular masculine nouns, which is not abbreviated as 1.o but as 1.er. And the same happens with tercer (an apocope of tercero) before singular masculine nouns, which is not abbreviated as 3.o but as 3.er. With compound ordinals ending in "primer" or "tercer", the same applies. For instance, "twenty-first" is vigésimo primer before a masculine noun, and its abbreviation is 21.er. Since none of these words should be shortened before feminine nouns, their correct forms for those cases are primera and tercera. These can be represented as 1.a and 3.a. (Note that, as with other abbreviations in Spanish, the ordinals require a fullstop, which is placed before the superscript letter(s).)
Numerals from 3 up form their ordinals uniformly by adding the suffix -ú: 3ú, 4ú, 5ú, etc. When the ordinal is written out, the suffix adheres to the spelling restrictions imposed by the broad/slender difference in consonants and is written -iú after slender consonants; but when written as numbers, only the suffix itself (-ú) is written. In the case of 4 (ceathair), the final syllable is syncopated before the suffix, and in the case of 9 (naoi), 20 (fiche), and 1000 (míle), the final vowel is assimilated into the suffix.
Most multiples of ten end in a vowel in their cardinal form and form their ordinal form by adding the suffix to their genitive singular form, which ends in -d; this is not reflected in writing. Exceptions are 20 (fiche) and 40 (daichead), both of whom form their ordinals by adding the suffix directly to the cardinal (fichiú and daicheadú).
The numbers 1 (aon) and 2 (dó) both have two separate ordinals: one regularly formed by adding -ú (aonú, dóú), and one suppletive form (céad, dara). The regular forms are restricted in their usage to actual numeric contexts, when counting. The latter are also used in counting, especially céad, but are used in broader, more abstract senses of 'first' and 'second' (or 'other'). In their broader senses, céad and dara are not written as 1ú and 2ú, though 1ú and 2ú may in a numeric context be read aloud as céad and dara (e.g., an 21ú lá may be read as an t-aonú lá is fiche or as an chéad lá is fiche).
|1||a haon||aonú (1ú) or céad|
|2||a dó||dóú (2ú) or dara|
|3||a trí||tríú (3ú)|
|4||a ceathair||ceathrú (4ú)|
|5||a cúig||cúigiú (5ú)|
|6||a sé||séú (6ú)|
|7||a seacht||seachtú (7ú)|
|8||a hocht||ochtú (8ú)|
|9||a naoi||naoú (9ú)|
|10||a deich||deichiú (10ú)|
The rule is to follow the number with the last letter in the singular and the last two letters in the plural. Most numbers follow the pattern exemplified by vint "20" (20è m sg, 20a f sg, 20ns m pl, 20es f pl), but the first few ordinals are irregular, affecting the abbreviations of the masculine forms. Superscripting is nonstandard.
One or two letters of the spelled-out numeral are appended to it (either after a hyphen or, rarely, in superscript). The rule is to take the minimal number of letters that include at least one consonant phoneme. Examples: 2-му второму /ftɐromu/, 2-я вторая /ftɐraja/, 2-й второй /ftɐroj/ (note that in the second example the vowel letter я represents two phonemes, one of which (/j/) is consonant).
When the numeral is followed by its head noun (which indicates the grammatical case of the ordinal), it is sufficient to write a period or full stop after the numeral: Päädyin kilpailussa 2. sijalle 'In the competition, I finished in 2nd place'. However, if the head noun is omitted, the ordinal indicator takes the form of a morphological suffix, which is attached to the numeral with a colon. In the nominative case, the suffix is ‑nen for 1 and 2, and ‑s for larger numerals: Minä olin 2:nen, ja veljeni oli 3:s 'I came 2nd, and my brother came 3rd'. This is derived from the endings of the spelled-out ordinals: ensimmäinen, toinen, kolmas, neljäs, viides, kuudes, seitsemäs, etc.
The system becomes rather complicated when the ordinal needs to be inflected, as the ordinal suffix is adjusted according to the case ending: 3:s (nominative case, which has no ending), 3:nnen (genitive case with ending ‑n), 3:tta (partitive case with ending ‑ta), 3:nnessa (inessive case with ending ‑ssa), 3:nteen (illative case with ending ‑en), etc. Even native speakers sometimes find it difficult to exactly identify the ordinal suffix, as its borders with the word stem and the case ending may appear blurred. In such cases it may be preferable to write the ordinal as a word (i.e., entirely with letters) instead – and particularly 2:nen is rare even in the nominative case, as it is not significantly shorter than if written as a word (toinen).
The general rule is that :a (for 1 and 2) or :e (for all other numbers, except 101:a, 42:a, et cetera) is appended to the numeral. When indicating dates, suffixes are never used. Examples: "1:a klass" (first (i.e. business) class), "3:e utgåvan" (third edition), but "6 november". Furthermore, suffixes can be left out if the number obviously is an ordinal number, example: "3 utg." (3rd ed). Using a full stop as an ordinal indicator is considered archaic, but still occurs in military contexts. Example: "5. komp" (5th company).
Similar conventions 
Some languages use superior letters as a typographic convention for abbreviations that aren't related to ordinal numbers – the letters o and a may be among those used, but they don't indicate ordinals:
- Spanish uses the indicator letters in some abbreviations, such as V.º B.º for visto bueno ("approved"); n.º for número, number; and M.ª for María, a Spanish name frequently used in compounds like José M.ª.
- In Portuguese, the underlined "º" and "ª" are used with many abbreviations, and should be preceded by a period. In fact, there is no limit for which words may be abbreviated this way. Sometimes, other letters are also written before the "º" or "ª". For example: Ex.mo for Excelentíssimo (an honorific), L.da for Limitada (Ltd.), Sr.a for Senhora (Ms.), etc.
- English has borrowed the "No." abbreviation from the Romance languages word numero (according to the OED, the term is from the Latin numero, which is the ablative form of the word numerus ("number"). Similar forms exist as the word for "number" is derived in other Romance languages: numero in Italian, numéro in French, and número in Spanish and Portuguese), applying it as an abbreviation for the English word "number". This is sometimes written as "Nº", with the superscript o optionally underlined; see numero sign.
Use of the ordinal-indicating Unicode characters for these kinds of abbreviations is a matter of preference, but can be misleading; the "º" in "Nº", for example, is not intended to indicate ordinality at all.
In Unicode 
- U+00AA ª feminine ordinal indicator (HTML:
- U+00BA º masculine ordinal indicator (HTML:
See also 
- Butterick, Matthew (October 4, 2012). "Typography for Lawyers - Ordinals". Retrieved 2012-10-04. "Bluebook rule 6.2(b)(i) (19th ed. 2010)"
- McMillan, Victoria E. (2011). Writing Papers in the Biological Sciences. Bedford/St. Martin's. p. 79. ISBN 9780312649715. Retrieved 2012-10-04.
- Microsoft® Manual of Style (4th ed.). Microsoft Press. 2012. p. 316. Retrieved 2012-10-04.
- Barr, Chris; Yahoo! (2010). The Yahoo! Style Guide. Macmillan. p. 359. ISBN 9780312569846. Retrieved 2012-10-04.
- "Automatic formatting results", Word Help, Office, Microsoft.
- Lynch, Jack (2012-10-04). The English Language: A User's Guide. Focus Publishing/R. Pullins Company. pp. 131, 213. ISBN 9781585101856.
Lynch, Jack (January 28, 2011). "Guide to Grammar and Style — M". Rutgers University. Retrieved 2012-10-04. "[...] ordinal numbers [...] no professionally printed books use superscripts [...]"
- Reindl, Donald F. 2009. "Kranjska je naša spraha: Historical German-Slovenian Language Contact." In: Stolz, Christel (ed.), Unsere sprachlichen Nachbarn in Europa: Die Kontaktbeziehungen zwischen Deutsch und seinen Grenznachbarn, pp. 103–114. Bochum: Universitätsverlag Dr. N. Brockmeyer, p. 110.
- "Latin-1 Punctuation codes" (PDF), Unicode.
- Ordinales, Royal Spanish Academy.
- "5. La grafia de les abreviacions" (PDF), Gramàtica de la llengua catalana, IEC, p. 391.
- "number words", Woordenlĳst (in Dutch).