You see it everywhere. It’s on your paycheck stub, your Instagram follower count, and that job posting you skipped because the "80k" salary felt a bit low for the stress involved. We just accept it. We don't even blink when someone says they’re running a 5k or buying a house for 400k. But wait—thousand starts with a T. So, why do we use a K? Honestly, the answer isn’t just some weird accounting quirk. It’s a linguistic inheritance from the Greeks that survived the Roman Empire and eventually conquered the digital world.
The Greek Connection: Where the K actually comes from
The "k" stands for kilo. Most people know that much. But kilo itself is a shortened version of the Greek word chilioi, which literally means "thousand." If you want to get technical—and we might as well—the ancient Greeks used chilioi to describe any large, indefinite number, but it eventually settled into the specific mathematical value of 1,000.
History is messy. The French are actually the ones we should thank (or blame) for making "kilo" a household term. During the late 1700s, right in the middle of the French Revolution, the guys in charge decided everything about the old way of measuring things was trash. They wanted a system based on logic and nature, not the length of some dead king’s foot. This gave birth to the Metric System in 1795. They took the Greek chilioi and shortened it to the prefix "kilo-" to represent a factor of one thousand. It was clean. It was efficient. It was very French.
Why is k for thousand used instead of T?
It seems logical to use T. It's the first letter of the word. However, "t" was already taken by the "ton" or "tonne," and in financial circles, "m" was already the Roman numeral for a thousand (mille). If you see an old-school accountant write $10M, they might actually mean ten thousand, not ten million. This creates a massive headache for everyone involved.
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Imagine the confusion. You think you're getting a million-dollar contract, but because of a Roman numeral hangover, you’re actually getting ten grand. Not great.
The "k" stepped in as a disruptor. Because "kilo" was part of the metric system—kilogram, kilometer, kiloliter—it became a universal shorthand that didn't conflict with the confusing Roman "M." It was distinct. You can't mistake a "k" for anything else in a ledger. By the time the 20th century rolled around, the "k" had jumped from the science lab to the stock market and eventually to your Twitter feed.
The 1960s and the computer revolution
When computers entered the scene, "k" became even more entrenched. Early programmers had a storage problem. Space was expensive. Why write "1,000 bytes" when you could write "1kb"? But here's where it gets a little nerdy: in the world of computing, a "k" isn't always exactly 1,000. Because computers speak in binary (base 2), a kilobyte is actually $2^{10}$ or 1,024 bytes.
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To solve this, some people tried to push "KiB" (kibibyte) for 1,024 and keep "kB" for exactly 1,000. Did it work? Sorta. Not really. Most of us just say "k" and call it a day. The convenience of a single letter won out over the precision of binary math.
The cultural takeover of the K
It’s not just for scientists anymore. We’ve internalized it. If you tell a teenager they have "1k" views on a video, they don't think about Greek etymology or the French Revolution. They just feel a hit of dopamine.
Interestingly, the use of "k" for money—like saying "that car costs 30k"—gained massive traction in the late 1970s and 80s during the rise of the Yuppie culture. It sounded faster. More professional. In the fast-paced world of trading floors, "k" was a syllable shorter than "thousand." Time is money, right?
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- Social Media: Followers, likes, and shares are almost always abbreviated with a K once they pass 999.
- Gaming: If you deal 5k damage in an RPG, you know exactly where you stand.
- Real Estate: Listings use "k" to keep signs readable from a moving car.
Is it possible we could have used "G" for Grand? Sure. People say "5 grand" all the time. But you never see someone write "My salary is 80G." It sounds like you're talking about gravity or a specific spot in the anatomy. "K" is just more polite. It's the neutral, go-to suffix for the modern era.
Why we aren't switching back
Languages are lazy. This isn't a bad thing—it's just how we evolve. Once a shortcut like "k" becomes globally recognized, the friction of changing it is too high. Think about it. We use "k" across almost every language that uses the Latin alphabet. It’s a rare piece of global consensus.
There are some holdouts. You’ll still see "M" for thousand in some very specific banking and oil-and-gas sectors (thanks to that Roman mille we talked about). If you’re looking at a financial statement and see "MM," that usually means "thousand thousands," which is a million. It’s confusing, it’s outdated, and it’s exactly why the "k" became so popular in the first place.
Actionable insights for using K correctly
If you’re writing, whether it’s an email to a boss or a caption on a photo, there are a few "unwritten" rules to keep your "k" usage from looking amateur.
- Don't capitalize unless you want to. In formal metric SI units, "k" for kilo is actually lowercase ($k$), while "M" for Mega is uppercase. However, in money and social media, "K" is often capitalized. Both are generally accepted now, but lowercase is technically more "scientific."
- Avoid the double-up. Don't write "$50k dollars." The "k" and the dollar sign already tell the story. "$50k" or "50,000 dollars" is the way to go.
- Know your audience. If you're dealing with old-school European accounting, double-check if they use "M" for thousand. It’s rare, but it can lead to some very expensive misunderstandings.
- Use it for scannability. In resumes and headers, use "k" to save space. It draws the eye and makes your achievements (like "Increased revenue by 40k") pop immediately.
The next time you see that "k" on a screen, remember you're looking at a 2,000-year-old Greek word that survived a French revolution and the birth of the internet just to tell you how many people liked your cat photo. It’s a weirdly durable piece of human history.