In general, write out numbers zero through nine. Use numerals for numbers 10 and above. Common exceptions include age, weight, monetary amounts, temperature, page numbers, scores and percentages.
Write out any number that begins a sentence.
Write out ordinal numbers (a number that indicates rank) under 10; use numerals for ordinal numbers 10 and above. Example: Drowning is the third leading cause of death of children ages 10-16. In 1965, it ranked 15th.
Use numerals for each number when two or more numbers appear in a sentence and 1 of them is 10 or larger. Example: Last month, 8 of the 16 geothermal sites were evaluated.
Use numerals (not words) until one million. Examples: 3,000 (not 3 thousand) 3 million (not 3,000,000)
Use Roman numerals (I, V, X, L, C, D and M) for wars and to show personal sequence for animals and people (World War II, Pope John Paul VI, King George III).
Write out simple fractions.
Use numerals for mixed fractions.
Write out fractions that are followed by a, of, or of an. Example: Almost one-fourth of the children in our community are overweight or obese.
Use numerals in fractions that are followed by a unit of measure. Example: The greenway segments are at least 4¼ miles apart.
Spell out amounts less than 1, using hyphens between the words: one-third, seven-eighths, etc. Use figures for precise amounts larger than 1. Example: According to the National Weather Service, we are 6 ¾ inches behind in rainfall.
Express percentages in numerals.
Use the percent symbol (%) or the word percent consistently within a document. Do not put a space between the number and the percent symbol (%).
Write out the word "cents" when writing about cents only (when not writing about dollars). Example: It costs 15 cents to recycle these items.
If the number expressing an amount of money is spelled out, so are the words dollars or cents. If numerals are used, they are accompanied by the symbol $ or ¢. Example: The average savings was $1 million.
Use numerals to refer to a span of years, but omit the first two digits of the second number. Example: Changes apply to the 2001-07 mechanical code standards.
Don't abbreviate the year. Use all four digits; don't omit the first two digits. Example: New investment in clean energy sources worldwide soared in 2008.
Write out the number associated with a century if the number is under 10. Use lowercase.
Write out decades in lowercase or use numerals. If you use numerals, do not use the apostrophe between the numerals and the "s". Example: Staff levels for the program are similar to those in the early '90s.
Use commas between groups of three digits, starting from the right, to show thousands, millions, etc. Example: More than 2,000 pounds of materials were recycled. Nearly 200,000 pounds are recycled annually.
Use a zero before a decimal point if there is no value in the first place to the left of the decimal.
Round to a whole number unless it is important to show the exact number.
Omit zeros after a decimal point unless they indicate exact measurement and the audience needs to know the level of significance.
Use hyphens between number groups so that a user can dial the number from a mobile device. Spaces and/or dots between number groups don't work in mobile.
Because area codes must be dialed in most cases, they should not be placed inside parentheses. Example: 704-336-7600