Spell out whole numbers between one and nine. In addition, any whole number that begins a sentence should be spelled out. Common fractions should be spelled out as well, such as three-quarters, for example.
Use Arabic numerals for all numbers 10 and over. Use numerals for all numbers in sentences that combine numbers below and above 10. For example: "I used to have 3 friends, but now I have 25."
Use numerals for any numbers that are decimals, including decimals less than 10. For example: 4.9.
Use numerals for all numbers in parenthetical citations, regardless of size. For example: "one author argues for a return to some, any type of responsible fiscal policy," (Smith, 1980, p. 4).
Use numerals for any numbers involving time, a person's age, dates, population size or amounts of money.
Follow the same rules for general numbers when using ordinal numbers. First, second, third, fourth, fifth, sixth, seventh, eighth and ninth are proper APA format. After ninth, switch to the use of numerals, such as 10th, 11th ... 192nd.