Why Is My Hard Drive Showing Less Space Than Advertised?
Last updated: January 2026
Your 6TB drive showing 5.45TB isn't defective or a scam. It's a decades-old clash between how drive manufacturers and operating systems count bytes.
The Short Answer
Drive manufacturers use decimal (base-10) units where 1 TB = 1,000,000,000,000 bytes.
Operating systems use binary (base-2) units where 1 TiB = 1,099,511,627,776 bytes.
Your drive has exactly as many bytes as advertised. Windows and macOS just display it using a different counting system.
TB vs TiB: The Full Explanation
This confusion exists because computers work in binary (powers of 2), but humans prefer decimal (powers of 10).
Decimal (what manufacturers use):
1 KB = 1,000 bytes
1 MB = 1,000,000 bytes
1 GB = 1,000,000,000 bytes
1 TB = 1,000,000,000,000 bytes
Binary (what your OS displays):
1 KiB = 1,024 bytes
1 MiB = 1,048,576 bytes
1 GiB = 1,073,741,824 bytes
1 TiB = 1,099,511,627,776 bytes
The "i" in KiB, MiB, GiB, and TiB stands for "binary" (kibibyte, mebibyte, gibibyte, tebibyte). These are the IEC standard names introduced in 1998 to clear up this confusion.
Unfortunately, Windows still labels binary values as "GB" and "TB" instead of "GiB" and "TiB", perpetuating the confusion.
How Much Space Will Your Drive Actually Show?
Here's what common drive sizes display in your operating system:
| Advertised | Actual Bytes | Shows As | "Missing" |
|---|---|---|---|
| 500 GB | 500,000,000,000 | 465.66 GB | 6.9% |
| 1 TB | 1,000,000,000,000 | 931.32 GB | 6.9% |
| 2 TB | 2,000,000,000,000 | 1.82 TB | 9.1% |
| 4 TB | 4,000,000,000,000 | 3.64 TB | 9.1% |
| 6 TB | 6,000,000,000,000 | 5.46 TB | 9.1% |
| 8 TB | 8,000,000,000,000 | 7.28 TB | 9.1% |
| 10 TB | 10,000,000,000,000 | 9.09 TB | 9.1% |
| 12 TB | 12,000,000,000,000 | 10.91 TB | 9.1% |
| 16 TB | 16,000,000,000,000 | 14.55 TB | 9.1% |
| 18 TB | 18,000,000,000,000 | 16.37 TB | 9.1% |
| 20 TB | 20,000,000,000,000 | 18.19 TB | 9.1% |
| 24 TB | 24,000,000,000,000 | 21.83 TB | 9.1% |
The "missing" percentage gets worse as drives get larger because the gap between 1000 and 1024 compounds at each unit level.
Can I Actually Store 6TB of Data on My 6TB Drive?
Yes, You Can
Your 6TB drive contains exactly 6,000,000,000,000 bytes (6 trillion bytes). That's exactly 6TB of storage using the manufacturer's definition.
If you have 6TB of files measured the same way, they will fit. The confusion is purely about how the number is displayed, not about actual capacity.
Think of it like measuring distance. A 100-kilometer drive is also 62.14 miles. You don't lose any road just because someone measured it differently.
Why Do Manufacturers Use Decimal?
Drive manufacturers aren't trying to deceive you. They use decimal because:
- It's the international standard — SI units (kilo, mega, giga, tera) are officially base-10
- It matches physics — drive platters don't naturally align to powers of 2
- It's been consistent since the 1980s — hard drives have always been marketed this way
- It's legally accurate — manufacturers clearly state "1 TB = 1,000,000,000,000 bytes" on packaging
Why Do Operating Systems Use Binary?
Computers fundamentally work in binary. Memory (RAM) is organized in powers of 2, and early programmers adopted binary prefixes because 1024 was close enough to 1000.
Back when drives were measured in megabytes, the ~5% difference didn't matter much. A 100 MB drive showing as 95 MB wasn't a big deal. But at the terabyte scale, 9% is hundreds of gigabytes.
macOS Changed in 2009
Starting with Snow Leopard, macOS switched to displaying decimal units. A 1 TB drive now shows as "1 TB" in Finder. Windows still uses binary units but labels them incorrectly as TB instead of TiB.
What About SSDs?
SSDs work exactly the same way. A 1TB SSD has 1,000,000,000,000 bytes and shows as 931 GB in Windows.
However, some SSD manufacturers slightly overstate capacity because SSDs reserve space for wear leveling and over-provisioning. A "1TB" SSD might have 1,024,000,000,000 bytes to account for this, but you'll only have access to 1TB after the reserved space is accounted for.
What About Formatted Capacity?
After formatting, you'll have slightly less space than even the binary calculation suggests. File systems need some space for:
- File system metadata — NTFS, ext4, and APFS all store organizational data
- Partition tables — GPT and MBR take a tiny amount
- Reserved blocks — ext4 reserves 5% by default (configurable)
This overhead is typically 0.1-1% on modern file systems, much smaller than the TB/TiB difference.
Bottom Line
You're not being cheated. Your drive has exactly as many bytes as advertised. The "missing" space is a display difference, not actual missing storage.
The math: Divide advertised TB by 1.0995 to get what Windows will display.
6 TB ÷ 1.0995 = 5.46 TB (shown in Windows)
When comparing drives, use our $/TB price tracker — we use the manufacturer's TB rating so all drives are compared fairly.