You're standing in the middle of a Home Depot, staring at a piece of lumber. Or maybe you're trying to figure out why your height looks weird on a digital form. You see a single tick mark. Then you see two. It’s a tiny detail, but honestly, it’s one of those things that creates a massive headache if you get it wrong in a blueprint or a math problem. What is the symbol for feet? Most people just call it an apostrophe, but that’s technically not the whole story.
In the United States and a few other places still clinging to the imperial system, we use the prime symbol ($′$) to denote feet. It looks like a slanted apostrophe. For inches, we use the double prime ($″$). If you’re typing on a standard QWERTY keyboard, you probably just hit the quote key. That works for a text message, sure. But if you’re a designer, an architect, or a math teacher, there’s a distinct difference between a "dumb quote" and a "prime." It’s the difference between looking like a pro and looking like you’re winging it.
The Short Answer: What is the Symbol for Feet?
The standard, most recognized symbol for feet is the prime symbol ($′$).
Most of the time, you'll see it written immediately following a number without a space, like 5′. If you are combining it with inches, it looks like 5′11″. We also use the abbreviation ft. Both are perfectly acceptable, but they serve different vibes. You use the symbol for technical drawings and quick notes. You use the abbreviation in formal writing or when you want to make absolutely sure there’s no room for a typo.
Here is the kicker: almost everyone uses the apostrophe (') on their keyboard because the actual prime symbol is buried deep in character maps. It’s a shortcut we’ve all agreed on. If you type 6'4" on a phone, everyone knows you're talking about height. Nobody is going to stop you. But if you're looking at a high-end typography layout or a professional architectural plan, that little slant in the prime symbol matters. It’s straighter and more angled than a curly "smart quote" that curves toward the text.
A History of Measuring with Our Limbs
Why do we even use this? The foot, as a unit of measurement, is ancient. Like, "older than the Roman Empire" ancient. Back then, people actually used their feet. Obviously, that was a disaster for trade because some guy named Claudius might have a size 12 while his neighbor has a size 8. Eventually, the English standardized it.
The prime symbol itself comes from the Latin prima divisio, meaning the first division of a unit. The double prime for inches comes from secunda divisio, the second division. It’s a logical hierarchy that has survived centuries of technological change. Even when the French went all-in on the metric system in the late 1700s, the US and the British Empire stuck to their guns. We kept our primes. We kept our feet.
Primes vs. Apostrophes: The Typographic Rabbit Hole
If you want to be a total nerd about it—and if you’re reading this, you probably do—you need to know about the "Straight Quote" problem.
- The Apostrophe/Single Quote ('): This is what you find next to your Enter key. In modern word processors like Microsoft Word or Google Docs, these often turn into "Smart Quotes," which curve.
- The Prime ($′$): This is a specific mathematical symbol. It doesn't curve. It’s a sharp, geometric stroke.
- The Abbreviation (ft): This is the safest bet for clarity.
If you use a curly apostrophe for feet ($6’$), it looks amateurish to a graphic designer. Why? Because curly quotes are designed to hug letters in a word like "don't." They aren't meant to sit next to numbers. In professional typesetting, using the wrong symbol is a "rookie mistake."
How to type the real symbol for feet
If you’re on a Mac, you can find the prime by hitting Control + Command + Space to bring up the character viewer. Search for "prime." On Windows, you’re stuck using Alt codes or the Character Map. For the average person, this is too much work. Just use the straight quote. Just make sure your software hasn't "helpfully" turned it into a curly one.
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The "ft" Abbreviation and International Standards
Let’s talk about the abbreviation ft. It’s the official ISO (International Organization for Standardization) way to do things when you aren't using the symbol.
- Singular: 1 ft
- Plural: 10 ft
Notice something? There is no "s." Writing "10 fts" is wrong. Writing "10 ft." (with a period) is common in the US, but international standards usually ditch the period unless it's at the end of a sentence. It’s cleaner. It’s faster. If you're writing a scientific paper, you’ll almost always use "ft" or stick to the metric system entirely because, let's be honest, the metric system is way easier for math.
The symbol for feet isn't universal. If you travel to Europe, you’ll see meters (m) and centimeters (cm). If you try to use the prime symbol there, people might think you're marking minutes or seconds of an arc in geography. That’s another place the prime lives: GPS coordinates. 34° 5′ 22″ means 34 degrees, 5 minutes, and 22 seconds. Imagine the chaos if you confuse a surveyor’s map with a construction blueprint. You’d be miles off target.
Common Mistakes to Avoid
People mess this up all the time. I've seen it on restaurant menus describing the "10' sub" (ten-foot sub? Probably not) and on real estate listings.
One big mistake is putting a space between the number and the symbol. It should be 6′, not 6 ′. Another is using the symbol for feet when you mean meters. It sounds silly, but in a globalized world, it happens.
Also, watch out for the "double-up." Don't write "6 ft′." Pick one. Either use the symbol or the letters. Using both is like wearing a belt and suspenders; it’s redundant and looks a bit confused.
Why does this still matter in 2026?
We live in a world of 3D printing and precision engineering. If you’re sending a file to a CNC machine or a laser cutter, symbols matter. Coding languages often use the single quote (') to define a string of text. If you're trying to input "5 feet" into a script and you use the symbol for feet, the computer might have a meltdown. It’ll think you’re starting a line of code instead of giving it a measurement.
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Actionable Steps for Using the Symbol for Feet
Stop stressing about the "perfect" prime symbol for everyday emails. The apostrophe is fine. But if you’re doing something that matters—like publishing a book, designing a sign, or submitting a technical drawing—follow these rules:
- Check your "Smart Quotes": Turn them off in your settings if you're typing measurements so they don't curl.
- Stick to "ft" for clarity: If there is any chance of a smudge or a digital glitch turning your $′$ into a $″$, just write out the letters.
- Consistency is king: Don't switch between 6′ and 6 ft in the same document. It looks messy.
- Know your audience: Architects love the prime. Scientists usually prefer the abbreviation.
When you're dealing with height, remember the format: 6′ 2″. No space between the number and the prime, but a small space between the feet and the inches is usually preferred for readability.
Next time you see a single tick mark on a blueprint, you'll know exactly what it is. It's not just a stray mark or a typo. It's the prime—the ancient, standardized symbol for feet that keeps our world from being measured in random, mismatched shoe sizes.