The complete form of 30 is thirty, which means 30, 30, 30, 3. 30th is its abbreviation, and the plural form is thirties.

Ordinal number is a kind of numeral, which is mainly mentioned in English grammar and expressed as "which number" in Chinese. In addition, in birthdays, ordinal numbers are also used to describe the date of birth.

1~30 ordinal number

1- 10: first, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth.

1 1-20: 11th, 12th, 13th, 14th, 15th, 16th, 17th, 18th, 19th and 20th.

2 1-30: 21st, 22nd, 23rd, 24th, 25th, 26th, 27th, 28th, 29th, 30th.