How Many MB in a GB: Why Your Computer and Your Hard Drive Disagree

You've probably seen it before. You buy a brand-new "1 TB" external drive, plug it into your Windows PC, and immediately feel cheated because the screen says you only have 931 GB. It’s annoying. You might think the manufacturer lied or that the drive is already half-full of "bloatware." Honestly, the answer to how many MB in a GB depends entirely on who you ask—a mathematician or a computer.

The short answer? 1 GB is either 1,000 MB or 1,024 MB.

That 24 MB difference seems like nothing. But when you scale it up to terabytes, we’re talking about losing nearly 70 GB of "perceived" space. This isn't just a rounding error; it’s a decades-old battle between two different ways of counting: Decimal and Binary.

The 1000 vs 1024 Showdown

Most of the world runs on the Metric system (SI). In that world, "kilo" means 1,000. Simple. "Mega" means a million. "Giga" means a billion. If you’re a hard drive manufacturer like Seagate or Western Digital, you use this decimal system. To them, 1 GB is exactly 1,000 MB. It makes the numbers on the box look bigger and keeps things consistent with how we measure weight or distance.

But computers are stubborn.

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They don't think in tens; they think in twos. Everything in a computer's brain is a series of "on" or "off" switches. Because of this, computers use the binary system (Base 2). For a computer, the closest "round" number to 1,000 is $2^{10}$, which is 1,024.

So, when your operating system—especially Windows—calculates storage, it uses 1,024 MB to make 1 GB. This is the root of your missing storage space. Your drive says "I have 1,000,000,000 bytes!" and your computer says "Cool, but I divide by 1,024, so to me, you're smaller."

Why Does This Even Happen?

Back in the early days of computing, the difference was tiny. 1,024 bytes vs 1,000 bytes was a 2.4% discrepancy. Engineers just called 1,024 a "Kilobyte" because it was close enough and "Kibi-byte" sounded ridiculous. But as we moved into Megabytes, Gigabytes, and now Terabytes, that 2.4% error compounded.

By the time you get to a Gigabyte, the gap between the two systems grows to about 7%. When you hit a Terabyte, you're looking at a 9% difference. This is why a 1 TB drive shows up as 931 GB. You aren't actually losing data; you’re just looking at two different "rulers" measuring the same thing.

The Language of "i": MB vs MiB

To try and stop the lawsuits—and yes, there have been massive class-action lawsuits over this—the International Electrotechnical Commission (IEC) stepped in years ago. They created new names to separate the two.

• MB (Megabyte): Exactly 1,000,000 bytes (Decimal).
• MiB (Mebibyte): Exactly 1,048,576 bytes ($1024 \times 1024$) (Binary).
• GB (Gigabyte): Exactly 1,000,000,000 bytes (Decimal).
• GiB (Gibibyte): Exactly 1,073,741,824 bytes ($1024 \times 1024 \times 1024$) (Binary).

If you use Linux or certain parts of macOS, you might see "GiB" or "MiB" pop up. Windows, however, is a bit of a rebel. Windows uses the binary calculation (1,024) but still labels it as "GB." It's technically incorrect labeling based on modern standards, but Microsoft has stuck with it for the sake of familiarity.

Real-World Examples: What Does 1 GB Actually Hold?

Forget the math for a second. Most of us just want to know if we can fit that movie or those photos on a thumb drive. If we assume the "standard" consumer definition where how many MB in a GB equals 1,000, here is what that looks like in 2026:

1. High-Res Photos: A modern smartphone photo is roughly 3–5 MB. You can fit about 250–300 of these in 1 GB. If you shoot in ProRAW, that number drops to about 15 photos.
2. Streaming Video: On Netflix or YouTube, 1 GB will get you about an hour of Standard Definition (480p) video. If you’re watching in 4K, you'll burn through a whole GB in about 7 to 10 minutes.
3. Music: A high-quality Spotify stream uses about 2.5 MB per minute. You’re looking at roughly 6–7 hours of music per GB.
4. Gaming: This is where the scale breaks. Modern games like Call of Duty or Cyberpunk updates can be 50 GB to 100 GB. That means a single game update can be 100,000 MB.

The RAM Exception

Here is a weird twist: RAM (Memory) always uses the 1,024 rule. Always. When you buy 16 GB of RAM, you are getting exactly $16 \times 1024$ MB. This is because memory chips are physically built in binary multiples. Unlike hard drives, which are just "buckets" of bits, RAM needs to be mapped in a way that the CPU can address, and CPUs speak binary.

How to Calculate It Yourself

If you’re trying to figure out if your file will fit, use these quick mental shortcuts.

To convert GB to MB (The "Marketing" way): Multiply by 1,000.
Example: 8 GB = 8,000 MB.

To convert GB to MB (The "Windows" way): Multiply by 1,024.
Example: 8 GB = 8,192 MB.

If you want to be super precise, use the formula for binary conversion:
$$Value_{MB} = Value_{GB} \times 2^{10}$$

Practical Takeaways for 2026

Stop worrying about the "lost" space on your drives. It’s not missing; it’s just a translation issue. If you’re a creative professional—say, a video editor or photographer—always buy 10% more storage than you think you need. This covers the "binary tax" that Windows will show you once the drive is plugged in.

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Also, pay attention to your data caps. Internet Service Providers (ISPs) almost always use the decimal (1,000) rule. If your cap is 1,000 GB, they are counting 1,000,000 MB. If your computer thinks you’ve only used 900 GB, you might actually be much closer to your limit than you realize because of that 7–9% discrepancy.

• Check your OS: Remember that Windows displays binary but labels it decimal.
• Buy larger: Assume a 1 TB drive will give you ~931 GB of usable space in Windows.
• Cloud storage: Most providers (Google, iCloud) use the decimal system, so 15 GB is 15,000 MB.

Next time you see a "low disk space" warning, you'll know exactly why those numbers don't seem to add up. You're just caught in the middle of a math war that's been going on since the 1970s.

Actionable Next Steps:

1. Audit your cloud storage: Check if your provider uses 1,000 or 1,024 to avoid surprise overages.
2. Format correctly: If you're moving files between Mac and PC, use ExFAT, but remember the reported sizes will still differ because of how each OS calculates the "how many MB in a GB" ratio.
3. Buffer your backups: When buying a backup drive for a 512 GB laptop, buy at least a 1 TB drive to account for the binary-to-decimal conversion and file system overhead.