You’re staring at a blueprint, a recipe, or maybe just a text message from a contractor, and there it is: that little double-tick mark. Most of us just call it the inches symbol and move on with our lives. But if you’ve ever seen a professional typographer cringe when you use a standard quotation mark instead of a proper prime, you know there’s more to the story. It’s one of those tiny details that separates a "quick draft" from a professional document. Honestly, it’s kinda wild how such a small glyph can cause so much confusion in technical drafting and digital publishing.
Most people think the inches symbol is just a double quote. It isn't.
What is the inches symbol actually called?
If we're being pedantic—and in the world of measurement, we usually have to be—the technical name for the symbol is the double prime. It looks like this: $''$.
In the vast majority of digital contexts, people just use the "smart quotes" or "dumb quotes" found on their keyboard. You know the ones. They’re the keys right next to the Enter button. But if you look closely at a high-end architectural drawing or a luxury watch catalog, those marks aren't curved. They don't "hug" the number. They are slanted, straight strokes. This distinction matters because, in the world of geometry and navigation, that same symbol represents seconds of arc.
Think about it this way. If you’re writing $45^\circ 30' 15''$, you’re describing a very specific point on a map. If you use curly "quote" marks there, the GPS software might just have a stroke. The double prime is a functional tool, not just a decoration.
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The difference between primes and quotes
We’ve all seen "smart quotes." They’re the ones that curve inward like little commas hanging in the air. Most modern word processors, like Microsoft Word or Google Docs, automatically turn your straight keyboard ticks into these curly beauties. It makes your essay look like a published book. That’s great for dialogue. It’s terrible for measurements.
The inches symbol should technically be straight or slightly slanted, but never curved. When you use a curly quote for 12”, you’re technically writing "12-end-quote." It looks amateur to a pro.
History of the tick mark
Where did this even come from? We have to go back way before computers. The use of prime marks ($'$) for feet and double primes ($''$) for inches likely evolved from the Latin primus and secundus.
- Foot = primus (first division).
- Inch = secundus (second division).
Basically, an inch is the "second" smaller division of a larger unit. This logic holds up in mathematics too. If you’re doing calculus, you use a prime mark to denote a derivative. If you’re a jeweler, you’re using these marks to denote the size of a setting. It's a universal shorthand that has survived the transition from stone tablets to ink to pixels.
Typing the inches symbol like a pro
Here is where it gets annoying. Your keyboard doesn't have a dedicated "double prime" key. It has a quote key. To get the actual, honest-to-god inches symbol, you usually have to dig into a glyph menu or use a specific Alt code.
On a Windows machine, holding Alt and typing 8243 on the number pad will sometimes give you the double prime, though it depends on the font. On a Mac, it’s often hidden in the "Emoji & Symbols" menu under "Technical Symbols."
But let's be real. Most of us aren't going to do that. If you're writing a casual email, just use the straight quote. The "dumb quote" (the one that isn't curly) is the universal substitute for the inches symbol. To get it in a doc that keeps auto-correcting to curly quotes, you usually have to hit "Undo" (Ctrl+Z) immediately after typing the quote. It’ll snap back to being straight. Magic.
Why it matters in 2026
You might think, "Who cares? It's just a mark." Well, search engines and AI models care. When you're searching for a 55" TV, the search engine has to recognize that " means inches and not the start of a quote about TVs.
In technical SEO and database management, using the wrong symbol can actually break a search query. If a database is looking for a numerical value followed by a double prime, and you've entered a curly Unicode quote, the system might not return the result. This is especially true in specialized fields like:
- CNC Machining: Where a fraction of an inch is the difference between a working part and scrap metal.
- Architecture: Where " means a specific distance on a scale.
- Graphic Design: Where typography defines the brand's authority.
Common Misconceptions
People often mix up the inches symbol with the symbol for feet. It's easy to do. Just remember: one tick for feet (because "foot" is shorter/simpler) and two ticks for inches.
Another weird one? The centimeter. Some people try to use the double prime for centimeters in European contexts. Don't do that. Centimeters are always "cm." The double prime is strictly for the Imperial system or for measuring angles in the form of "seconds."
Actionable steps for your documents
If you want your work to look like it was written by an expert rather than a bot, start paying attention to your ticks. It’s a small change with a big impact.
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First, disable "Smart Quotes" in your settings if you are writing a technical manual or a list of product dimensions. In Google Docs, go to Tools > Preferences > Substitutions and uncheck the smart quotes box. This ensures your inches symbol stays straight and professional.
Second, if you are a web designer, use the HTML entity ″ for the actual double prime and ′ for the foot mark. It’s cleaner for screen readers and looks much sharper on high-resolution displays.
Third, always put a space between the number and the symbol? Actually, no. That’s a common mistake. In standard style guides like the NIST or the Chicago Manual of Style, the symbol should sit right up against the number. It’s 12", not 12 ".
Lastly, check your fractions. If you're writing 1/2", try to use the actual fraction glyph (½") if your font supports it. It looks significantly better and is much easier for a reader to process at a glance. Small tweaks like these are what make a document "human-quality" in a world of generic, auto-generated text.