The Slash: Rules for Using It Correctly

What is a slash?

A slash is used in several situations and serves a variety of functions in publications. Above all, it can replace certain conjunctions such as “or”, separate alternatives such as “and/or”, and stand in for the preposition “per” or “a” in expressions such as km/h.

Using a slash also requires knowledge of certain typographic rules concerning spaces. In some cases, a space is used after the slash, or both before and after it—for example, and/or usually has no spaces, while transfer / credit card may use spaces to separate phrases. In other cases, spaces should not be inserted.

When should you use a slash?

You probably use the slash fairly often, usually without thinking about it. But are you sure you are using it correctly?

In English, the slash is used in a number of recurring situations, including the following:

1. Replacing “or”. A slash separates alternative words or expressions, such as pass/fail or input/output.
2. Combining “and” and “or”, as in and/or, his/her or buyer/seller. In formal writing, however, it is often better to rewrite the sentence to avoid ambiguity.
3. Marking successive periods, such as the academic year 2025/26 or the nineteenth/twentieth century.
4. Marking line breaks in a quoted poem or song when the lines are written in running text, for example: “The moon climbed high / Across the sky.”
5. Replacing “per” or “a” in measurements and rates, such as 10 g/l, 90 km/h or $5/day.
6. Writing common fractions, such as 1/4 or 3/4. In professionally typeset text, these may instead appear as fraction characters such as ¼ and ¾.
7. Writing addresses, particularly where a slash separates a unit or apartment number from a building number, such as 12/34 King Street. Follow the convention used in the relevant address system.
8. Describing document and reference numbers, such as Ref. A-17/2024 or File 106/17.
9. Marking abbreviations from other languages, such as c/o (“care of”) or a/a (“against the advice of”, in some professional contexts).
10. Separating numbers in a combined publication issue, such as issue 2/3, or in bibliographic references, such as No. 3/2019.

When should you avoid using a slash?

A slash is sometimes used incorrectly, especially in situations that resemble those in which it is appropriate. This makes errors easy to miss. You can avoid them by following the rules below.

Incorrect uses of the slash:

• Writing dates without following a consistent style, for example mixing 12/24/2022, 24/12/2022 and 2022/24/12. Choose one accepted format for your audience, such as 24 Dec 2022 or 2022-12-24.
• Writing mixed numbers ambiguously, such as 1 1/4 in a context where the fraction could be misread. Use a properly formatted fraction or write it out as one and a quarter.
• Replacing “and” between names, such as Kaye/Godwin when the intended form is the compound name Kaye-Godwin.
• Creating nonstandard abbreviations, such as Springfield n/Chicago. Write the relationship out or use an established abbreviation, such as Springfield near Chicago.

Slash with or without spaces: the rules

In some cases, using a slash requires a space beside it, while in others it does not. It may seem confusing that a space can appear after the slash or on both sides of it. The rules are simpler than they may seem.

You only need to remember 3 rules about spaces:

• Do not use spaces when the slash separates single words or numbers, such as up/down, 2025/26 or and/or.
• Use spaces when the slash separates longer phrases, such as bank transfer / credit card, or when it marks a line break in a quoted poem: “The moon climbed high / Across the sky.”
• You may use a space after the slash or on both sides of it, depending on the style and context. The important thing is to remain consistent throughout the text.