How to Make 'RBI' Plural

Mignon Fogarty
1-minute read


I know the NBA playoffs are happening, and the Stanley Cup Final is happening, but the boys of summer are on the field too. Baseball season has started, so it’s a good time to answer questions from listeners who have asked how to make an abbreviation such as RBI plural. It can be confusing, since it's the R-part (run) that is becoming plural. Should it be RsBI or RBIs or something else?

Even though it doesn't make absolute logical sense, you make initialisms and acronyms plural by adding an S to the end no matter what part would be plural if you wrote the whole thing out: even though it would be runs batted in, you write it RBIs.

Can Use an Apostrophe with an Acronym?

In the past, some publications used apostrophes to make acronyms and abbreviations plural, so until a few years ago, it was common to see something like RBI's or CD's in the New York Times. Today, all major publications and style guides I'm aware of recommend simply adding an S (without an apostrophe).

When Do You Use Periods with Acronyms?

Whether you put periods after the letters in an acronym such as NASA or an initialism such as RBI is a style choice, but neither the Chicago Manual or Style nor the AP Stylebook recommend using periods.

Mignon Fogarty is the author of 101 WORDS TO SOUND SMART.

About the Author

Mignon Fogarty

Mignon Fogarty is the founder of Quick and Dirty Tips and the author of seven books on language, including the New York Times bestseller "Grammar Girl's Quick and Dirty Tips for Better Writing." She is an inductee in the Podcasting Hall of Fame, and the show is a five-time winner of Best Education Podcast in the Podcast Awards. She has appeared as a guest expert on the Oprah Winfrey Show and the Today Show. Her popular LinkedIn Learning courses help people write better to communicate better.