What do the United States, Liberia, and Myanmar have in common? Not much, but we are the only countries in the world that don’t use the metric system. Regardless of your opinion in the metric/English debate, we often find ourselves using both standards on a daily basis, often in the same document or report. Logically, these different standards need different formatting.
In text, metric units should be abbreviated (millimeters becomes mm) while English units are spelled out. When abbreviated in text, English units can confuse readers. While you may recognize “gal in oz” as gallon, inch, and ounce, some readers may immediately think of Dorothy and the yellow brick road.
When used in a table, English units can be abbreviated to save space. When using a compound English measurement (e.g. feet per second [ft/s]) introduce the abbreviation the first time it is used, and then continue using it throughout the text.