Why a 2TB drive looks like 1.8TB
Drive makers sell capacity in decimal units, the SI convention. NIST states that SI prefixes refer strictly to powers of 10. That makes 1 gigabyte exactly 1,000,000,000 bytes and 1 terabyte 1,000,000,000,000 bytes. A "2TB" drive therefore holds about 2,000,000,000,000 bytes.
Many software displays divide those same bytes by powers of 1,024 instead. A binary gigabyte is 1,073,741,824 bytes, and a binary terabyte is 1,099,511,627,776 bytes. NIST's guidance also says plainly that kilo, mega and giga must not be redefined as 1,024-based quantities. The standards-correct names for the binary units are kibi, mebi, gibi and tebi (Ki, Mi, Gi, Ti), which NIST lists as the recommended prefixes for powers of 2.
The arithmetic works out like this:
- 1,000,000,000,000 bytes ÷ 1,073,741,824 is about 931.3 GiB.
- A 2TB drive is about 1,862.6 GiB, or about 1.82 TiB.
- Windows commonly labels those values "GB" and "TB". That is why a 1TB drive reads about 931GB and a 2TB drive reads about 1.82TB.
The bytes are all still there. Only the unit changed.
How fast the gap grows
Each step up the prefix ladder multiplies the 1,024-versus-1,000 difference. The gap in unit size is about 2.4% at kilo, 4.9% at mega, 7.4% at giga and roughly 10% at tera (more precisely, 2^40 / 10^12 is about 1.0995). That is why the shortfall was a rounding annoyance in the megabyte era and is a visible 9% haircut at terabyte scale. Typical results:
| Label on the box | Typical Windows readout |
|---|---|
| 500GB | about 465GB |
| 1TB | about 931GB |
| 2TB | about 1.81–1.82TB |
| 4TB | about 3.63TB |
| 8TB | about 7.27TB |
One caution: this 9% is a difference in unit size. It is not a share of the drive's physical capacity that has been held back.
What Microsoft's own forums say
A Microsoft Q&A thread on the gap between total bytes and the GB figure shows the effect on a real readout. An independent advisor explained that Windows divides by 1,024 three times. In the example, 29,288,968,192 bytes works out to 27.27GB under that calculation. The same answer notes that a 1TB drive appears as 931GB.
A second, AI-generated answer on that page makes the same point. It says Windows labels base-2 units as KB, MB, GB and TB. Dividing by 1,000,000,000 would instead give about 29.29GB. Both answers are community or automated responses, not a Windows specification. They are useful corroboration of the practical example, and they do not prove that every Windows screen behaves the same way.
I could not verify from primary documentation that Windows 11 applies this convention everywhere. The safest reading is that some Windows displays report byte totals in binary-sized units under decimal-style labels. Other tools may differ.
macOS flipped the display, which shows this is a choice
Apple documents the decimal-versus-binary split on its support pages. Apple's packaging says 1GB equals 1 billion bytes and 1TB equals 1 trillion bytes, with formatted capacity being less. Apple also says some apps and operating systems, such as OS X Leopard and earlier, report capacity in binary.
Apple changed course with Snow Leopard in 2009. Coverage of Apple's knowledge-base article at the time reported that Snow Leopard displays storage capacity per product specifications (base 10). A 200GB drive then shows 200GB in Finder's Get Info. The change happened in August 2009, when Snow Leopard shipped.
That settles the "who is right" question. Both are valid when the unit is stated clearly. Apple picked the display that matches the box, and Windows kept the display it had.
I'm not verifying the original claim about Linux here. Whether a given Linux tool shows decimal or binary units depends on the tool, so check the specific tool's documentation.
Why Windows is unlikely to change
Changing the label would break something else. The same GB label is used for RAM, where capacity is naturally binary. If Windows reported memory in decimal units, a 16GB RAM kit would read about 17.2GB (16 × 1,024³ ÷ 1,000³). Switching everything to GiB and TiB would be technically clean, but it would confuse many users.
A split like macOS's, with decimal for storage and binary for memory, is possible. It would still change what long-time Windows users and scripts expect to see. The claim that this will "remain a problem forever" is rhetorical, not a technical prediction. It is a deeply entrenched convention. It would only change if Microsoft and the wider software ecosystem decided the confusion outweighed the disruption.
Separate from the unit issue: space that really is used
Two different things get blended together here, and they should be kept apart:
- Unit conversion: the same bytes shown in a different unit. Nothing is lost.
- Space actually consumed: formatting structures, extra partitions, the OS and preinstalled software.
Microsoft's deployment documentation on disk layouts shows how a typical system disk is divided. A bootable drive needs a system partition. The Windows partition holds the OS, and a separate recovery tools partition sits alongside it. That documentation says the recovery image (winre.wim) is typically around 250–300MB, depending on drivers, languages and customizations. It also notes that the file system itself can take extra space. Those amounts are small next to a multi-terabyte drive.
Prebuilt PCs can carry several gigabytes of preinstalled software, as the original reporting notes. How much is used varies by machine, so don't assume a fixed loss on every new SSD.
How to check your own drive
If a "2TB" SSD shows 1.82TB, you can confirm that nothing is wrong:
- Find the exact byte capacity of the volume or disk. Windows property sheets also show a byte count.
- Divide it by 1,000,000,000,000 to get decimal TB, which should be near the advertised number.
- Divide it by 1,099,511,627,776 to get TiB, which should be near what Windows displays as TB.
- Open Disk Management and compare the disk size against the volumes. Look for unallocated space, a system or recovery partition, or a leftover layout from a previous install.
- If the gap is much bigger than the unit math predicts (for example, a "2TB" drive showing under 1.7TB), look at partitions and the drive's own reporting rather than assuming the conversion explains it.
Bottom line
A 2TB SSD that reads about 1.82TB in Windows is behaving normally. The box counts in powers of 10 and some Windows displays count in powers of 2. Compare byte counts, not labels. If the number is far below the unit math, check partitions before you suspect the drive.