In general, use numerals to express numbers 10 and above, and use words to express numbers zero through nine.

there were 15 psychologists at the clinic

the study had 40 participants

students were in the third, sixth, eighth, 10th, and 12th grades

However, there are exceptions to this general guideline for number usage. There are cases in which you should always use numerals to express numbers, even numbers zero through nine, and likewise, there are cases in which you should always use words to express numbers, even numbers 10 and above.

Numbers expressed in numerals are covered in Section 6.32 of the APA Publication Manual, Seventh Edition

Cases in Which to Always Use Numerals for Numbers

Always use numerals to express numbers in the following cases, even numbers zero through nine: 

Case

Example

Numbers that immediately precede a unit of measurement

5-mg dose

3 cm

Statistical or mathematical functions

multiplied by 2

Fractions or decimals (except common fractions)

1.5

2.27

Percentages

50%

75%–80%

Ratios 4:1 ratio

Percentiles and quartiles

the 5th percentile, the 95th percentile

the 3rd quartile

Times and dates (including approximations of time)

30 s

10 min

3 hr

2 days

approximately 4 months

2 years

about 6 years ago 

3 decades

12:30 a.m. 

6 p.m. (or 6:00 p.m.)

Ages

5 years old, 18 years old

5-year-olds, 18-year-olds

5-year-old children, 18-year-old adults

Scores and points on a scale

scored 6 on a 7-point scale

Exact sums of money

$10

$50 in U.S. dollars

Numerals as numerals

the numeral 2 on the keyboard

Numbers in a Series

Also use numerals to write numbers that denote a specific place in a numbered series when the number comes after the noun (e.g., Step 1). The noun before the number is also capitalized. This guideline applies to parts of books and tables as well (e.g., Chapter 1).

However, when the number comes before the noun, the usual guidelines for number use apply, as in the following examples.

Number after a noun

Number before a noun

Year 5

the 5th year

Grade 5, Grade 11

the fifth grade, the 11th grade

Step 1

the first step

Level 4

the fourth level

Items 3 and 5 the third and fifth items

Question 2, Question 25

the second question, the 25th question

Table 2, Figure 5

the second table, the fifth figure

Column 8, Row 7

the eighth column, the seventh row

Chapter 6, Chapter 14

the sixth chapter, the 14th chapter

Exceptions: Do not capitalize the abbreviations for page(s) or paragraph(s), even when they are followed by a numeral (e.g., p. 3, pp. 2–5, para. 9, paras. 1–4).