Generally, spell out numbers 10 and under and certain round multiples of those numbers.
Regardless of magnitude, treat numbers dealing with the same category consistently in the same paragraph or even section.
The company has three facilities, nine pipelines, and fifteen wells.
Or: The company has 3 facilities, 9 pipelines, and 15 wells.
But never: The company has three facilities, nine pipelines, and 15 wells.
Never start a sentence with a numeral. If it’s too awkward to spell out the number, restructure the sentence.
Never use apostrophes to signal the plural! Just add an s.
He only flies on 747s. [never 747’s]
Formatting of long numbers follows SI standards (see section 5.4.4 of the SI brochure):
Numbers with four digits have no space or comma.
5000
Numbers with five or more digits have nonbreaking spaces (not commas) separating groups of three digits. (See the Tools of the Trade section for how to access special characters.)
50 000; 5 000 000
In columns where work is totalled and in tables, the numbers are aligned right, and even four-digit numbers have a space to align with the others.
5 000
17 000
9 234 700
9 256 700
Numbers with decimals must have a whole number or zero before the decimal point.
0.25, not .25
Both in running text and in tables, prefer the symbol % to spelling it out (which is done as two words, per cent).
Spell fractions out or, if they’re attached to a whole number using numerals, use decimals.
Times New Roman has three proper fractions, which you could use sparingly: ¼, ½, and ¾.
Never just use a slash in running text to create an arbitrary fraction (e.g., 7/8). The editors can help you if you have a special circumstance.
Use only hyphens with phone numbers. Do not enclose the area code in parentheses.
403-123-4567; 1-800-222-3333