Guidelines for Writing Numbers on the Web from the Yahoo! Style Guide

There are certain situations in which numerals are always correct and others in which numbers must be spelled out. This handy-dandy list is a basic quick reference for the appropriate format for writing numbers on the Web according to the Yahoo! Style Guide.

Always use numerals for the following:

• Age of people: Use hyphens when age is used as a compound adjective (a 5-year-old boy). Do not use hyphens if it stands alone (He is 5 years old.) For more examples, click here.

• Money: Use the $ and numeral without a space between ($65). Do not use .00 for whole dollar amounts unless it will help create consistency in a list or table (small $2.50, medium $3.00, large $3.50). For amounts less than a dollar use the word cents after the number (69 cents). More examples and information about designating currency type (only if absolutely necessary for clarity) can be found, here.

• Time: Use a.m. or p.m. (no spaces, just periods). On the hour numerals can stand alone (3 p.m.) the :00 is a waste of Web space. When using a.m. and p.m. using the phrases like in the morning or at night takes up space and is redundant. Don't do it. Use all caps for time zones (EST) if necessary. More about time is available here.

• Instructions or steps (Please, press 1). Enough said.

• Numbers expressed in millions or billions: 5 billion, not five billion.

• Sports Scores and votes: separate by hyphen (no spaces) 5-4. Always lead with winning count. Also use numerals to express leads (The A-Team is up by 2).

• Passwords, codes and long strings of numbers.

• Dimensions: Always use numerals for measurements. There are several correct ways to designate dimensions; using symbols, abbreviations or spelling out the units of measure. Consistency is the key. Do it the same way throughout your writing. Punctuation will vary depending on how you denote dimensions. Find out more here.

Otherwise spell out numbers one through nine, and use numerals for numbers 10 and up unless:

• The above list applies to the number in question.

• Another number referring to the same category of information within the same passage is greater than 10. Use numerals for all to create consistency (There were 3 [not three] participants out of 15 who did not complete the test).

• Numbers at the beginning of a sentence have to be spelled out. It is punishment for beginning a sentence with numbers, which is generally a bad idea. The only exception is years, which doesn't really belong at the beginning of a sentence either.

The Yahoo! Style Guide gives you some style options depending on your target audience, for example using abbreviations to streamline mobile content. It is important to choose based on your target audience and to use the same style throughout. I have found it helpful to choose one of the correct ways of writing numbers and applying it consistently every time I write for the Web.

Headlines allow a little more leniency in using numerals because of space considerations. Generally it isn't necessary to spell out numbers in a headline, but caution is needed to make sure the headline is strong and clear.

More detailed information about using numbers can be found at the Yahoo! Style Guide online.

http://styleguide.yahoo.com/