Numbers Wikipedia:Manual of Style

wp:manual of style/dates , numbers (mos:num) § numbers clarifies number of situations, including following:

in general, write whole cardinal numbers 1 9 words, write other numbers that, when spoken, take 2 or fewer words either figures or words (with consistency within each article), , write other numbers figures: 1/5 or one-fifth, 84 or eighty-four, 200 or 2 hundred, 3.75, 544, 21 million. see mos:num § numbers figures or words et seq. exceptions , fine points.
in general, use comma delimit numbers 5 or more digits left of decimal point. numbers 4 digits @ editor s discretion: 12,345, either 1,000 or 1000. see mos:num § grouping of digits et seq. exceptions.
in general, use decimals rather fractions measurements, latter permitted measuring systems such imperial units , u.s. customary units. keep articles internally consistent.
scientific notation (e.g., 7007580000000000000♠5.8×10 kg) preferred in scientific contexts; editors can use {{val}} template, generates such expressions syntax {{val|5.8|e=7|u=kg}}.
write out million , billion on first use. after that, unspaced m can used millions , bn billions: 70m , 25bn. see mos:num § numbers figures or words similar words.
write 3%, 3 percent, or 3 per cent, not 3 % (with space) or three %. percent american usage, , per cent british usage (see § national varieties of english, above). in ranges of percentages written en dash, write single percent sign: 3–14%.
indicate uncertainties (value ± uncertainty) × 10ⁿ units , e.g., 7023153400000000000♠(1.534±0.35)×10 m. see mos:num § uncertainty , rounding other acceptable formats.