How to write and publish a scientific paper - Barbara Gastel, Robert A. Day 2022

Units of measurement
How and when to use abbreviations
Scientific style

Units of measurement are abbreviated when used with numerical values. You would write “4 mg was added.” (The same abbreviation is used for the singular and the plural.) When used without numerals, however, units of measurement are not abbreviated. You would write “Specific activity is expressed as micrograms of adenosine triphosphate incorporated per milligram of protein per hour.”

Careless use of the diagonal slash can cause confusion. This problem arises frequently in stating concentrations. If you say that “4 mg/ml of sodium sulfide was added,” what does this mean? Does it mean “per milliliter of sodium sulfide” (the literal translation), or can we safely assume that “per milliliter of reaction mixture” is meant? It is much clearer to write “4 mg of sodium sulfide was added per milliliter of medium.”