Spell out all ordinal numbers in text.
Not recommended: 1st, 5th, 12th, 43rd
Recommended: first, fifth, twelfth, forty-third
Numbers as words
In general, spell out the following:
- Numbers from zero through nine, except as noted below in Numbers as numerals.
A number that starts a sentence.
Recommended: Fifteen directories are created.
In some cases it's better to rearrange the sentence so that the number appears later.
Not recommended: 164 MB is generally considered too large a file to send as an attachment.
Recommended: In general, avoid sending files larger than 164 MB as attachments.
Exception: It's okay, but non-optimal, to begin a sentence with a four-digit year.
A number that is followed by a numeral.
Recommended: This procedure creates fifteen 100,000-byte files.
Recommended: This procedure creates 15 of the 100,000-byte files.
Indefinite and casual numbers.
Recommended: You can specify thousands of combinations.
Recommended: The API might return a list of a million songs.
Numbers as numerals
In general, use numerals for the following:
Numbers 10 and greater.
Exceptions: Always use numerals for the following items, even if they're less than 10:
- Version numbers.
- Technical quantities, such as amounts of memory, amounts of disk space, numbers of queries, or usage limits.
- Page numbers.
- Chapter numbers, sections, pages, and so on.
- Numbers without units, such as numbers used in mathematical expressions.
Numbers less than 10 when they appear in the same sentence with numbers greater than 9.
Recommended: The menu contains 15 options but 6 of them are disabled.
- Negative numbers.
- Most fractions.
For decimal numbers less than one, place a zero in front of the decimal point.
Recommended: 0.3 inch
- Numbers in a range.
- Express fractions as decimal numbers, when possible.
When expressing fractions as words, connect the numerator and denominator with a hyphen unless one of them is already hyphenated.
Recommended: five sixty-fourths
In general, use numerals and the percent sign (%), without a space between them.
Exception: If the percentage starts the sentence, then spell out both the number and the word percent.
Recommended: Forty percent of the files
Ranges of numbers
Use numerals for ranges.
In theory, the correct punctuation for a range of numbers is an en dash. But in practice, for simplicity we use a hyphen with no space either side of it.
See also the Hyphens page.
- two-day total
- version 3
- four options
- five minutes
- 6 queries/second
- 8 pixels
- nine developers
- 10 chapters
- 18 years old
- 27 minutes
- 50 MB/s
- 102 degrees
- 728 shipments
- 18,000,000 users
For information about formatting quantities like 10 MB, see Units of measurement.
Commas and decimal points in numbers
Use commas and decimal points in accordance with standard American number-formatting.
Specifically: in numbers four or more digits long, use commas to set off groups of three digits, counting leftward from the decimal point, in the standard American style. For long decimal numbers, do not use any digit-group separators to the right of the decimal point.
Use a period for a decimal point, also in the standard American style.
Examples of comma grouping
Not recommended: The limit is 1532784 bytes per day.
Recommended: The limit is 1,532,784 bytes per day.
Not recommended: The API supports up to 2000 vertices.
Recommended: The API supports up to 2,000 vertices.
Not recommended: $0.031 611 / vCPU hour
Recommended: $0.031611 / vCPU hour
For more about decimal points and digit group separators, see Wikipedia's decimal mark entry.
Use numerals for dimensions.
Use a lowercase x between the numerals in the dimensions, with no space between the numerals and the x.
Not recommended: 192 x 192