Numbers

Ages:

Except in formal writing, definite ages should be expressed in numerals:

                         10 years old, a lad of 5 years, 47 years old

                         Formal: Many people retire at age sixty–five.

Dates:

In very formal writing (invitations, etc.), the date is spelled out:

                         Saturday, May sixth, one thousand nine hundred and eighty–nine
                                                               or
                         Saturday, May sixth, nineteen hundred and eighty–nine

In letters and informal writing shorten the date:

                         Saturday, May 6, 1989

Decimals and Percentage:

Use numerals to express decimals. When expressing a decimal that is not preceded by a whole number, add a zero to the left of the decimal point 
(period) unless the first digit to the right is a zero:
                        
                         23.7765      0.897       0.6       .0076

You may use numerals to express percentages, but always spell out a percentage at the beginning of a sentence:                     

                        We were over 80 percent in attendance.
                                                 —BUT—
                         Eighty percent were in attendance.

In tabulations, memos, etc., use % instead of spelling out "percent":

                        We lost 80% of our office staff to the recent flu epidemic.

Dimensions, Distance, Measure, Temperature, Weight:

In formal writing use numerals to express units of:

                         Dimension:      5 by 8 feet
                                                    -NOT-
                                            5 x 8 feet or 5' by 8'

                         Distance:          25 miles
                                                    -BUT-
                         Spell out a fraction of a mile (a quarter of a mile).

                         Measure:           5 pints, 25 gallons, 10 bushels, 3 liters
                                
                         Temperature:    105° F,   25° C

                         Weight:            16 grams, 3 ounces, 40 pounds, 105 tons

In less formal writing, abbreviate, but do not capitalize:

                         10 ft 5 in            30 mi           100 yd      10 lbs 4 oz

In technical writing use ' for feet, " for inches, and x for by:

                         6' x 9'      6' 8" x 3' 4"

Fractions:

Where possible, fractions should either be spelled out or expressed as decimals :

                         a quarter of an acre — 0.25 acre — 1/4 acre 
                                                        —NOT—
                         0.25 of an acre — 1/4 of an acre — 1/4th acre
                                                                                                                                                                   
When a fraction is the subject of a sentence, the verb must agree with the noun in the prepositional phrase:

                         Nine–tenths of the people were late.
 
                         Three–fourths of the plant was damaged.

General:

In formal writing, numbers should be spelled out unless they are very long:

                         ten, fifty, ninety–nine
                                       -BUT-           
                                       5,280

Never start a sentence with a numeral. When possible, rephrase a sentence to begin with another word. Otherwise, spell it out:

                         Ten dollars was enough for a pretty good time back then.

                         Back then, one could have a pretty good time for ten 
                         dollars.

Spell out approximations:

                         about a hundred miles, approximately four pounds

Spell out round numbers:

                         one hundred, a million, five thousand

Spell out numbers from one through ten, except in related series:

                         2 ducks, 5 geese, 7 chickens, and 10 hogs
 
When related numbers appear within a sentence, be consistent in expressing them:

                         15 gallons of gas for each 100 miles
                                                      or
                         fifteen gallons of gas for each one hundred miles

But, when numbers appear together, spell out the shorter of the two:

                         10 twenty–cent cigars, a hundred 1975 Mustangs

Use numerals to express exact amounts and/or long numbers:

                         246 passengers; 1,658,400 light years from Earth

Money:

In formal writing small amounts of money should be spelled out:

                         ten dollars, two hundred dollars, fifty cents

In less formal writing, and when expressing larger amounts, use numerals:

                         50 million dollars or $50 million;

                         $2.5 million or two and a half million dollars;

                         $2.75 billion; $750,000; $1,500; $675.50
           
Use ¢ for cents only when there are no dollars in the amount:

                         50¢ (same as $.50)      5¢ (same as $.05)  
                                                
                         But never use both:     $1.50¢

Page Numbers & Roman Numerals:

Always use numerals for page numbers:

                         page 3,  page 649

Table of Roman numerals:

1–I; 2–II; 3–III; 4–IV; 5–V; 6–VI; 7–VII; 8–VIII; 9–IX; 10–X

11–XI; 14–XIV; 19–XIX; 20–XX; 30–XXX 40–XL; 50–L; 60–LX; 70–LXX; 80–LXXX

90–XC; 100–C; 200–CC; 300–CCC; 400-CD; 500–D; 600–DC; 900–CM; 1000–M 
                                                                                    
4000–MV; 5000–V; 10,000–X; 100,000–C; 1,000,000–M; 1989–MCMLXXXIX 

Time:

In formal writing spell out the time of day:

                         eight in the morning, five o'clock that night

In letters, memos, instructions, etc., use numerals to express time:

                         8 a.m. or 8 A.M.              4:45 p.m. or 4:45 P.M.

Do not add zeros to even hours unless a time containing minutes appears in the same sentence:
        
                         The first train arrives at 8 a.m.

                         The trains will arrive hourly from 8:00 a.m. until 5:30 p.m.

Spell out decades and centuries:

                         those fabulous sixties, the sixteenth century