Numerals

AP Stylebook: Numerals
In general, spell out one through nine. Use figures for 10 or above and whenever preceding a unit of measure or referring to ages of people, animals, events, or things.

Decimals

AP Stylebook: Decimals
If a unit of measure follows the numeral, use the decimal format, not fractions.

1.75 mg (NOT 1 3⁄4 mg)

2.5 kg (NOT 2 1⁄2 kg)

If the value is less than 1, insert a zero before the decimal point.

0.2 g (NOT .2 g)

0.9 mg/kg

Fractions

AP Stylebook: Fractions
Spell out common fractions. Insert a hyphen only if the fraction modifies a noun.

Examples:

Patients had adverse reactions to the medication in one third of the cases.
A two-thirds majority is needed.

Ordinals

Ordinals generally express ranking rather than quantity, so spell out first through ninth, and use the numeral for 10th and above. Do not use superscript for ordinals.

Examples:

The fourth patient was admitted in critical condition.
The 12th patient died shortly after his arrival.

When you have a mixture of ordinals below and above nine, use numerals. This is a divergence from AP Style. 

Example: The 5th and the 12th patients showed similar symptoms.

Percent, percentage, percentage points, %

AP Stylebook: Percentages

Singular and plural

When the quantity is less than 1, the unit of measure is singular.

Examples:

0.5 gram (NOT grams)

0.2 second (NOT seconds)

Spacing

Insert a space between the numeral and the symbol, except for %, °C, °F, ° (for angles),
money symbols, fractions, and inches/feet symbols.

25 g
30%
£250

40 mL
28.5°C
CHF 50*

60 kg
4"
5 ½ years

*a space is added because CHF is the abbreviation for the Swiss Franc currency and not a symbol.

Units of measure

Abbreviated units of measure do not have a period, unless they close a sentence.

Examples:

50 mg (NOT 50 mg.)

2 dL (NOT 2 dL.)