You just plugged in that shiny new 1TB hard drive and Windows tells you it only has 931GB of space. You feel cheated. You're not alone. This isn't a manufacturing defect or a hidden partition eating your storage. It's a math problem that has been annoying computer users since the late nineties. The core of the confusion is a tiny "i" that most people ignore.
Understanding how much is one GiB—that’s a gibibyte, not a gigabyte—requires a quick trip into how computers actually think versus how humans prefer to market things.
The short answer: 1,073,741,824 bytes
Basically, one GiB is exactly $2^{30}$ bytes. If you're looking for a comparison you can actually use, it is about 1.074 gigabytes (GB).
Computers are binary. They love powers of two. For a machine, it’s much easier to group things in 1,024s than in 1,000s.
Humans? We’re different. We have ten fingers. We like the metric system. For us, "giga" means a billion—one followed by nine zeros. When a hard drive manufacturer puts "1TB" on a box, they mean 1,000,000,000,000 bytes. But your operating system (specifically Windows) calculates that same pile of bytes using the binary method.
Why does the GiB vs GB distinction exist?
Back in the early days of computing, the difference was negligible. A kilobyte was 1,024 bytes, and everyone just shrugged and called it 1,000 because the 2.4% error didn't matter much when you were dealing with tiny files.
As storage exploded, that "small" error compounded. By the time we hit gigabytes, the gap grew to over 7%.
In 1998, the International Electrotechnical Commission (IEC) stepped in to fix the mess. They created new terms like kibibyte (KiB), mebibyte (MiB), and gibibyte (GiB) to specifically represent the binary (base-2) versions. Under these rules:
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- A Gigabyte (GB) is exactly 1,000,000,000 bytes (decimal).
- A Gibibyte (GiB) is exactly 1,073,741,824 bytes (binary).
Honesty time: almost no one uses these terms in casual conversation. You don't ask your friend if their phone has 256 "gibibytes" of storage. You say gigabytes. But your computer? It's thinking in GiB even if it's lying to you on the screen by using the "GB" label.
Real-world math: Converting GiB to other units
If you're trying to figure out exactly how much data you're working with, you've got to know which system you're in.
One GiB is equal to 1,024 MiB.
It is also 1,048,576 KiB.
If you want to convert how much is one GiB into the standard gigabytes (GB) used by marketers, you multiply the GiB value by 1.0737.
Let's look at a practical example. Say you have a game download that is 50 GiB. To find out how much space that takes on a drive marketed in GB, you do the math: $50 \times 1.073741824$. That's roughly 53.7 GB.
The Windows "Confusion" Factor
Windows is arguably the biggest culprit in keeping this confusion alive. It measures your RAM and hard drive space in binary (GiB) but labels the output as "GB."
macOS and Linux (mostly) have moved on. Since Snow Leopard (OS X 10.6), Apple has used the decimal system. If you buy a 500GB drive and plug it into a Mac, it actually says 500GB. Plug that same drive into a Windows machine? It says 465GB.
The drive didn't shrink. The ruler just changed.
Why developers and gamers care about GiB
In gaming and software development, GiB is the only unit that matters for performance. Memory addresses are binary. When a developer says a game needs 8GB of RAM, they actually mean 8GiB ($8 \times 1,024 \times 1,024 \times 1,024$ bytes).
If you're building a PC, you'll notice that RAM is always sold in binary increments: 8GB, 16GB, 32GB. These are actually 8GiB, 16GiB, and 32GiB. Because RAM is tied directly to the CPU's ability to address memory, it must follow the power-of-two rule.
Cloud providers like AWS, Azure, and Google Cloud also use GiB for billing. If you provision a "100GB" volume on some services, you're actually getting 100GiB. This is a subtle win for the consumer because 100GiB is actually about 7% more storage than 100GB.
How to check what you actually have
If you want to see the "true" byte count on a Windows machine to settle the GiB vs GB debate for yourself, it’s easy.
- Open File Explorer.
- Right-click on your C: drive.
- Select Properties.
- Look at the Capacity line.
You will see a massive number in bytes, followed by a smaller number in "GB." If you take that massive byte number and divide it by 1,073,741,824, you will get the exact GiB number Windows is showing you.
Actionable Takeaways
Stop feeling like you're being scammed by hard drive companies. They are actually using the "correct" SI definition of "giga," even if it feels misleading.
When you're buying storage, always assume you'll have about 7-10% less "usable" space than what’s on the box if you're a Windows user. A 1TB drive (1,000GB) will always show up as roughly 931GiB.
If you are a developer or system admin, start using the "i" in your documentation. Writing GiB instead of GB prevents rounding errors that can crash systems when you're pushing the limits of a disk's capacity.
Next time you see how much is one GiB, just remember the number 1,024. It’s the magic key to the binary world. Everything in that world—KiB, MiB, GiB—is just 1,024 of the unit below it.
To get an accurate estimate of your "real" Windows space before buying a drive, multiply the advertised capacity by 0.931. This simple trick will save you the headache of wondering where your missing gigabytes went.